Medical implants having desired surface features and methods of manufacturing

ABSTRACT

In embodiments of the invention, an implant that anchors into bone may have a bone-facing region that comprises a plurality of interconnected struts. The interconnected struts may define local features such as engagement ridges, fins, crests, a macroscopic surface-interrupting feature, a divertor structure, and sawteeth in any combination. Such features may help resist translation or rotation of the implant, and may be conducive to bone ingrowth. Parameters such as local empty volume fraction and local average strut length can be varied, even within the features, by the design of the network of struts. Struts may be tapered. Cantilever struts may also be provided, which may point in a desired direction. The pattern of struts may be specified to the level of dimensions and location of individual struts. The implant may be manufactured by additive manufacturing methods. The mesh of struts may be generated by an algorithm using Voronoi tessellation.

CROSS-REFERENCE TO PRIOR APPLICATION

This application is a continuation of, and claims priority to andbenefit under 35 U.S.C. § 120 to U.S. application Ser. No. 15/043,081,filed Feb. 12, 2016, now patent Ser. No. 10/098,746 which claimspriority to and benefit under 35 U.S.C. § 119(e) to the U.S. ProvisionalApplication Ser. No. 62/116,211, filed on Feb. 13, 2015, the entirecontents of which are incorporated herein by reference.

FIELD OF THE INVENTION

Embodiments of the invention pertain to medical implants that interfacewith bone.

BACKGROUND OF THE INVENTION

Implants that interface with natural bone need to form a strongmechanical bond with the natural bone, both at the time of implantationand after bone growth onto or into the implant has occurred. Variousgeometries and manufacturing techniques for implants are known. Someimplants have used rough or porous surfaces or coatings that areconducive to ingrowth or ongrowth of bone. However, it is stilldesirable to improve the design and manufacture of implants, and toencourage bone growth and formation of a strong mechanical bond betweenthe implant and the bone.

SUMMARY OF THE INVENTION

In an embodiment of the invention, there may be provided an implantabledevice, comprising a first region that is substantially solid; and asecond region, adjacent to the first region, the second regioncomprising a plurality of interconnected struts, some of the strutsjoining the first region, the struts having an average strut length, thestruts defining openings between the struts through which bone can grow,wherein the second region comprises struts that are connected at both oftheir ends to other struts and are outermost struts and define anexterior having a bone-facing enveloping surface, and wherein thebone-facing enveloping surface has at least one concavity and at leastone convexity.

In an embodiment of the invention, there may be provided an implantabledevice, comprising a first region that is substantially solid; and asecond region, adjacent to the first region, the second regioncomprising a plurality of interconnected struts, some of the strutsjoining the first region, the struts having an average strut length, thestruts defining openings between the struts through which bone can grow,wherein the second region comprises struts that are connected at both oftheir ends to other struts and are outermost struts and define anexterior having a bone-facing enveloping surface, and wherein the secondregion has a variation of local empty volume fraction within the secondregion, or the second region has a variation of local average strutlength within the second region, or both.

In an embodiment of the invention, there may be provided an implantabledevice, comprising a first region that is substantially solid; and asecond region, adjacent to the first region, the second regioncomprising a plurality of interconnected struts, some of the strutsjoining the first region, the struts having an average strut length, thestruts defining openings between the struts through which bone can grow,wherein the second region comprises struts that are connected at both oftheir ends to other struts and are outermost struts and define anexterior having a bone-facing enveloping surface, and wherein at leastsome of the struts are tapered along their length.

In an embodiment of the invention, there may be provided an implantabledevice, comprising a first region that is substantially solid; and asecond region, adjacent to the first region, the second regioncomprising a plurality of interconnected struts, some of the strutsjoining the first region, the struts having an average strut length, thestruts defining openings between the struts through which bone can grow,wherein the second region comprises struts that are connected at both oftheir ends to other struts and are outermost struts and define anexterior having a bone-facing enveloping surface, wherein the secondregion further comprises a plurality of cantilevers that extend outwardfrom vertices at or near the local enveloping surface and extend beyondthe bone-facing enveloping surface, and wherein each of the cantilevershas a respective lengthwise cantilever direction, and at each of thecantilevers there is a respective local normal vector that is normal tothe local enveloping surface of the implantable device at a location ofthe cantilever, and the cantilever direction points more towards a rearof the implantable device than does the local normal vector.

In an embodiment of the invention, there may be provided an implantabledevice, comprising a first region that is substantially solid; and asecond region, adjacent to the first region, the second regioncomprising a plurality of interconnected struts, some of the strutsjoining the first region, the struts having an average strut length, thestruts defining openings between the struts through which bone can grow,wherein the second region comprises struts that are connected at both oftheir ends to other struts and are outermost struts and define anexterior having a bone-facing enveloping surface, and wherein theimplantable device further comprises a plurality of cantilevers thatextend outward from the first region.

In an embodiment of the invention, there may be provided an implantabledevice, comprising a first region that is substantially solid; and asecond region, adjacent to the first region, the second regioncomprising a plurality of interconnected struts, some of the strutsjoining the first region, the struts having an average strut length, thestruts defining openings between the struts through which bone can grow,wherein the second region comprises struts that are connected at both oftheir ends to other struts and are outermost struts and define anexterior having a bone-facing enveloping surface, and wherein theimplantable device further comprises a plurality of loop structures, theloop structures being curved or segmented and connecting at both oftheir ends to vertices, the loop structures extending beyond thebone-facing enveloping surface.

In an embodiment of the invention, there may be provided an implantcomprising a first region that is substantially solid; and a secondregion, adjacent to the first region, the second region comprising aplurality of interconnected struts, some of the struts joining the firstregion, the struts having an average strut length, the struts definingopenings between the struts through which bone can grow, wherein thesecond region comprises struts that are connected at both of their endsto other struts and are outermost struts and define an exteriorenveloping surface, wherein the exterior enveloping surface has a smoothregion that is generally smooth on a size scale greater than the averagestrut length, and wherein the exterior enveloping surface also has,extending outward from the smooth region, at least one sharp featurethat is sharp on a size scale of the average strut length or smaller,wherein the sharp feature and the smooth region are both made of some ofthe plurality of the struts.

In an embodiment of the invention, there may be provided an implantcomprising a first region that is substantially solid; and a secondregion, adjacent to the first region, the second region comprising aplurality of interconnected struts, some of the struts joining the firstregion, the struts having an average strut length, the struts definingopenings between the struts through which bone can grow, wherein thesecond region comprises struts that are connected at both of their endsto other struts and are outermost struts and define an exterior having abone-facing enveloping surface, wherein the bone-facing envelopingsurface has at least one concavity and at least one convexity.

In an embodiment of the invention, there may be provided an implantcomprising a first region that is substantially solid; a second region,adjacent to the first region, the second region comprising a pluralityof interconnected struts, some of the struts joining the first region,the struts having an average strut length, the struts defining openingsbetween the struts through which bone can grow; and the second regionhaving a second region external enveloping shape at a size scale largerthan an average strut length, wherein the implant has a longitudinalaxis and, in a cross-section taken perpendicular to the longitudinalaxis, has a perimeter, wherein at some places the perimeter is fartherfrom the longitudinal axis than the perimeter is at other places, by atleast one of the average strut length.

In an embodiment of the invention, there may be provided an implantcomprising a first region that is substantially solid; a second region,adjacent to the first region, the second region comprising a pluralityof interconnected struts, some of the struts joining the first region,the struts having an average strut length, the struts defining openingsbetween the struts through which bone can grow; and wherein the secondregion comprises struts that are connected at both of their ends toother struts and are outermost struts and define an exterior envelopingsurface, wherein at least some of the struts connect at respective endsto others of the struts at vertices, wherein the second region externalshape has a majority external enveloping surface occupying a majority ofan exterior of the second region, wherein the second region externalshape further comprises a macroscopic surface-interrupting feature thatdiffers from the majority external enveloping surface, wherein themacroscopic surface-interrupting feature comprises some of theinterconnected struts.

In an embodiment of the invention, there may be provided an implantcomprising a first region that is substantially solid; and a secondregion, adjacent to the first region, the second region beingrough-surfaced or porous or comprising a plurality of interconnectedstruts, wherein on an exterior thereof, the implant comprises a fin thathas a fin long direction, and wherein, on the exterior, the implantfurther comprises a divertor structure, wherein the divertor structureis located rearward from the fin along a direction of advancement theimplant, wherein the divertor structure is not in line with the finalong the fin long direction.

In an embodiment of the invention, there may be provided an implantcomprising a first region that is substantially solid; and a secondregion, adjacent to the first region, the second region comprising aplurality of interconnected struts, some of the struts joining the firstregion, the struts having an average strut length, the struts definingopenings between the struts through which bone can grow, whereinexternal-most struts that connect at both ends to other struts define,at a size scale larger than the average strut length, a local envelopingsurface, wherein the second region further comprises a plurality ofcantilevers that extend outward from vertices at the local envelopingsurface, wherein each of the cantilevers has a respective lengthwisecantilever direction, and at each of the cantilevers there is arespective local normal vector that is normal to the local envelopingsurface of the implant, and the cantilever direction points more towardsa rear of the implant than does the local normal vector.

In an embodiment of the invention, there may be provided an implantcomprising a first region that is substantially solid; and a secondregion, adjacent to the first region, the second region comprising aplurality of interconnected struts, some of the struts joining the firstregion, the struts having an average strut length, the struts definingopenings between the struts through which bone can grow, whereinexternal-most struts that connect at both ends to other struts define,at a size scale larger than the average strut length, a local envelopesurface, further comprising a plurality of cantilevers that extendoutward from vertices at the enveloping surface, wherein the implant hasan external shape that is at least approximately a hemisphere having anequator and a pole, and the cantilevers exist at or near the equator ofthe implant but a region closer to the pole of the implant is free ofthe cantilevers.

In an embodiment of the invention, there may be provided an implantcomprising a first region that is substantially solid; and a secondregion, integrally joined to the first region, the second regioncomprising a plurality of interconnected struts in a predeterminedgeometry that fully defines a location of each of the struts, the strutsbeing at least approximately straight, wherein at least some of thestruts connect to others of the struts at vertices, wherein thepredetermined geometry of the plurality of the struts is non-repeating.

In embodiments of the invention, an implant having a first region thatmay be a non-bone-facing region and a second region that may be abone-facing region may be designed containing thousands of struts in thesecond region such that the design specifies the location, placement,and dimensions of each strut. The implant may be manufactured tocorrespond to the design, within manufacturing tolerances, and multipleimplants may be manufactured that are substantially identical to eachother, within manufacturing tolerances. The manufacturing may be done byadditive manufacturing, which may be from powder as a starting material.Joining of powder particles to other powder particles or toalready-manufactured parts of the implant may be done by laser or byelectron beam or by other means. It is described in embodiments of theinvention that the detailed design of the pattern of the struts may besomewhat random and non-repeating. The struts may form a network into oronto which bone can grow. Struts may connect to other struts atvertices. Features that are designed into the pattern of struts (such asengagement ridges, fins, sawteeth, crests etc.) may be made ofinterconnected struts that smoothly interconnect with the strut patternof the second region in general. Thus the second region, formed byinterconnected struts, may have an overall shape and also have specificlocal features all defined by a network of interconnected struts. Theinterconnected-strut region (second region) and the first region, whichis more solid, may be made in a single manufacturing process, and infact with a layer-by-layer manufacturing process, manufacturing such asfusing performed in a given layer may be devoted in one portion of thelayer to making solid or nearly-solid material corresponding to a firstregion, while in another portion of the same layer, the manufacturingsuch as fusing may be devoted to making portions of struts.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

Embodiments of the invention are further described in the followingillustrations.

FIG. 1 is a perspective view of a generic hip implant, including anacetabular cup.

FIG. 2A illustrates placement of the features of an embodiment of theinvention, on an acetabular cup or shell of a hip prosthesis.

FIG. 2B is an enlargement of a portion of FIG. 2A, illustrating both afirst region that is fully dense and a second region that comprises aplurality of struts.

FIG. 2C is similar to FIG. 2B but illustrating placement of the featureson a femoral stem component of a hip prosthesis.

FIG. 2D is similar to FIG. 2B but is an even closer-up view of an arrayof struts.

FIG. 3A is an external view of a shape such as a generally hemisphericalshape having a feature that may be referred to as an engagement ridge,which extends in a circumferential direction around the circumference ofthe implant.

FIG. 3B is a cross-section of FIG. 3A.

FIG. 4A is a three-dimensional view of a hemispherical implant that hasextending therefrom a fin of somewhat rectangular cross-sectional shape.

FIG. 4B is a sectional view of FIG. 4A.

FIG. 4C is a three-dimensional view of a hemispherical implant that hasextending therefrom a fin of somewhat triangular cross-sectional shape.

FIG. 4D is a bottom view of FIG. 4C

FIG. 5A is an outline of a second region for a shape such as a generallyhemispherical shape having a macroscopic surface-interrupting featurethat is a somewhat gradual shape, added onto a majority external surfaceshape. For clarity of illustration, in FIG. 5A, individual struts arenot shown.

FIG. 5B is an external view of a shape as described in FIG. 5A. FIG. 5Bshows, for the second region 200, individual struts both at the exteriorand within the region.

FIG. 5C shows a surface that is generally hemispherical but the envelopeof the struts on its exterior has flat facets.

FIG. 5D shows a surface that is generally hemispherical but the envelopeof the struts on its exterior has segments that are curved approximatelycylindrically.

FIG. 6A is a three-dimensional view of a generally hemisphericalexternal shape having fins that also have sawteeth on their exteriors.

FIG. 6B is a side view of FIG. 6A.

FIG. 6C is a side view of one fin of FIG. 6B, more closely showing thesawteeth.

FIG. 6D is a top view showing just the placement of fins, withoutshowing details of sawteeth.

FIG. 6E is a bottom view showing just the placement of fins, withoutshowing details of sawteeth.

FIG. 6F shows a fin that has sawteeth and shows a plurality ofinterconnected struts that make up the fin and the sawteeth on the fin.

FIG. 7A is a perspective view of an embodiment having fins and divertorstructures.

FIG. 7B shows a bottom view of an embodiment of the invention, having agenerally hemispherical exterior shape and having both fins and divertorstructures, with only the divertor structures being visible in thebottom view.

FIG. 7C shows a top view of the same embodiment.

FIG. 7D shows a side view of a portion of a side view of the view ofFIG. 7C.

FIG. 7E is an enlarged view of the central portion of FIG. 7D.

FIG. 8A is a three-dimensional perspective view of an array ofinterconnecting struts in which, on the left, the struts are of constantcross-section along their length, and, on the right, some of the strutsare tapered along their length.

FIG. 8B shows the same situation as FIG. 8A, in the form a top view.

FIG. 8C shows the same situation as FIG. 8A, in the form a side view.

FIG. 9 is an external view, generally along an axis, showing the levelof detail of individual struts, both exterior and interior, of animplant that has cantilevers on the exterior. This is a view of the meshstructure, with the solid interior omitted for clarity of illustration.

FIG. 10A is a similar external view, but three-dimensional andsectioned, showing cantilevers. In this illustration, the solid interiorregion is present.

FIG. 10B is a schematic illustration of cantilevers on a generallyhemispherical shape, wherein the cantilevers point generally backwardwith respect to the direction of insertion of the implant, toward anequator of the implant.

FIG. 11 is an illustration of cantilevers on fins, at the level ofdetail of showing individual struts.

FIG. 12 is an illustration of cantilevers on sawteeth, at the level ofdetail of showing individual struts.

FIG. 13A is an illustration of cantilevers joining to an equatorial bandsolid region at the edge of the strut-containing region.

FIG. 13B is an illustration of cantilevers extending from a smallportion of an equatorial band solid region.

FIG. 13C is an illustration of cantilevers extending from most of anequatorial band solid region.

FIG. 14 is an illustration of cantilevers that are bent.

FIG. 15 is an illustration showing loop structures.

FIG. 16 shows a stem geometry having an engagement ridge.

FIG. 17A shows a stem geometry having a fin.

FIG. 17B shows a stem geometry having periodic crests around itsperimeter, formed from an array of interconnected struts.

FIG. 17C shows a stem geometry having cantilevers.

FIG. 18A shows a stem geometry having, around its perimeter, a variationof average strut length and a variation of empty volume fraction in theregion that has an array of interconnected struts.

FIG. 18B is a sectional view of FIG. 18A.

FIG. 19 shows an implant having a concave bone-facing surface, such asmight be used for resurfacing a joint.

FIG. 20A shows a rasp assembled together with its handle.

FIG. 20B shows the rasp and handle of FIG. 20A, with the rasp slightlyseparated from its handle.

FIG. 20C is a close-up view of the rasp.

FIG. 21A is a three-dimensional perspective view showing an acetabularcup.

FIG. 21B is a similar view of the terminal adapter.

FIG. 21C is a similar view showing the terminal adapter about to becoupled to the acetabular cup.

FIG. 21D shows the assembled acetabular cup and terminal being insertedinto an incision in an approximately sideways orientation.

FIG. 21E shows the assembled acetabular cup and terminal already insidethe surgical site and reoriented to an orientation that is approximatelyits final orientation.

FIG. 21F shows a situation similar to that of FIG. 21E, but with aninstrument coupled to the terminal adapter such as for purposes ofpushing the acetabular cup into its final position.

FIG. 22A is an illustration of a Voronoi tessellation in a plane.

FIG. 22B is a cross-section of a three-dimensional Voronoi tessellation.

DETAILED DESCRIPTION

Referring now to FIG. 1, there is illustrated a conventional jointreplacement prosthesis, which in this illustrated example is for a hipjoint replacement prosthesis. Such a prosthesis may comprise a ballelement or ball assembly and a cup element or cup assembly that canreceive the ball element or ball assembly. As illustrated, the ballassembly may be an assembly in which a ball and a stem are manufacturedindividually and are then assembled to each other. Alternatively, theball and the stem may be manufactured integral with each other. Each ofthe two elements or assemblies may be shaped suitably to anchor torespective bone. As illustrated, one element or assembly is suitable toanchor into a long bone having a central canal, and this element orassembly has an elongated stem. As illustrated, another element orassembly is shaped to anchor into a relatively massive piece of bone,and this element or assembly has an external shape that is somewhatconvex without being significantly elongated. As illustrated, theprosthesis comprises one each of an element or assembly whosebone-engaging shape is elongated and an element or assembly whosebone-engaging shape is non-elongated. However, it is also possible thata joint prosthesis in general could have both elements/assemblies beingelongated, or, both elements/assemblies being non-elongated. Asillustrated, the elongated bone-engaging shape is associated with theball assembly, and the non-elongated bone-engaging shape is associatedwith the cup assembly. However, other variations are also possible.Typically, at least some of these components may comprise a metal suchas titanium or a titanium alloy, but other materials are also possible.

For a hip prosthesis, typically the cup element or assembly may beimplanted in the acetabulum of the pelvis, and the ball element orassembly may be implanted into the canal of the femur. Replacement jointprostheses are also possible for various other joints of the body, andmay have similar parts such as cups and stems, but the orientations ofthe ball and the cup may vary, and the geometry of interaction with boneon respective sides of the joint may vary such as being elongated or notelongated as appropriate. In known prostheses, the external, bone-facingsurface of an implant may also comprise, on a small size scale such onthe order of 1 mm or less, an irregular pattern that is conducive toingrowth or ongrowth of bone. Examples of such irregular pattern includea coating, or a sintered geometry, or other type of surface ortexturing. The material of the bone-facing surface or coating ortexturing may be either the same as the material of other parts of theimplant, or a different material.

A cup element may be used in conjunction with a liner that is receivedinside the cup and that may have its own internal concave shape thatreceives the ball. Such a liner may be made of a polymeric material, oralternatively a ceramic material or other material.

Regions and Struts

Referring now to FIGS. 2A-2C, it is illustrated that in an embodiment ofthe invention, there may be provided an implant 10 that includes a firstregion 100 and a second region 200. As illustrated, the second region200 may be a bone-facing region. The first region 100 may be a regionthat is somewhat removed from bone. For example, a cup type implantmight have a convex exterior, and the second region 200 may face bone,and the first region 100 may be substantially solid metal, which mayitself have a cup-shaped interior. As another example, a stem typeimplant may have second region 200 that faces bone, and first region 100may be the interior of the stem. More generally, at least some of thefirst region 100 may face away from bone.

The first region 100 may be fully dense, meaning that it is entirelysolid material. In a similar sense, it is possible that the first region100 might not be perfectly fully dense, and yet may be close enough tofully dense so that it functions similarly to fully dense material, suchas in terms of structural strength. For example, depending on themanufacturing process, it is possible that the first region 100 mightcontain occasional small inclusions or voids containing a gas such asair, or even vacuum. The first region 100 may contain a modest number ofinternal voids that do not connect to the interface between the firstregion 100 and the second region 200, or alternatively or in addition itcould even have a small number of voids that do connect to the interfacebetween the first region 100 and the second region 200. As an example,the first region 100 could have a local density that is greater than 90%of the solid density that the same material would have in a completelysolid condition.

The implant 10 may further comprise a second region 200 that comprises aplurality of struts 300. The second region 200 may be on the external orbone-facing side of the implant 10, relative to the first region 100.The second region 200 may be structurally connected to the first region100. The second region 200 may comprise an array of interconnectedstruts 300. Some of the struts 300 may be connected to the first region100. The second region 200 may further include within itself empty spacebetween the struts 300, that is, space that is not occupied by any ofthe struts 300.

A strut 300 may generally be a component that has an identifiabledirection of greatest dimension and is structurally connected to atleast one other strut 300 or to first region 100. Strut 300 may have twoidentifiable end points. Struts 300 may be straight but need not beexactly straight. A strut 300 may have along its length a region ofsomewhat constant cross-section, but this is not essential. A strut 300may also have an enlarged region that can be thought of as a meniscusnear an end of a strut 300 or where the strut 300 connects to anotherstrut 300 or to first region 100. A strut 300 may have a centerline thatdefines a path of points that are centroids of cross-sections of thestrut 300, with the centerline going generally along the identifiabledirection of greatest length of the strut 300. It can be noted that thedepiction of a strut 300 shown in FIG. 2 may be an idealization of ashape of actual struts, and the same comment applies to other Figures aswell. Some of the struts 300 may be connected to the first region 100,while other struts 300 may be connected to still other struts 300without being connected to the first region 100. The second region 200may have at its external surface a mesh of struts 300 at its surfacedefining an identifiable external or imaginary enveloping surface.Struts 300 that define the enveloping surface may be struts that connectat both of their ends to other struts.

In connection with the description of cross-sectional properties ofstruts, it is further possible that a strut may have a taper from one ofits ends to its other end such that the cross-sectional area of thestrut is larger toward one end of the strut than it is toward the otherend of the strut. For example, the end of the strut having the largercross-sectional area may be joined to or may be closer to the solid orsubstantially solid first region 100. Such a tapering feature mayprovide a gradual transition of strength, a less abrupt transition thanwould be the case for untapered struts. If struts are tapered asdescribed, not all struts have to be so tapered. In terms ofcross-sectional shape, struts may be approximately cylindrical (roundcross-section), or triangular prismatic (triangular cross-section), orof rectangular cross-section, or generally any desired cross-sectionalshape.

An array of struts 300 may define, between the struts 300, open spacesin which bone can grow, such that eventually bone can grow to surroundthe struts 300 and embed the struts 300 in bone. A “vertex” is definedto be the intersection point where two or more struts 300 meet,specifically where the centerlines of the respective struts 300intersect with each other.

In embodiments of the invention, the locations of the struts 300 may bepredetermined and defined to such a degree of detail and exactness thatthe same pattern of struts 300 could be manufactured repeatedly anynumber of times, resulting in any number of manufactured items that aresubstantially identical to each other even at the level of detail of thenumber of struts and the location, orientation, interconnection patternand dimensions of every strut 300.

As is further discussed elsewhere herein, the implant 10 can be thoughtof as an integral manufactured piece some of which is solid and some ofwhich is a region that contains a certain amount of empty space betweenand among struts 300. As discussed elsewhere herein, struts 300 may havea variety of lengths within a given implant.

As a non-limiting example, the second region 200 can have a thickness ofseveral lengths of typical struts 300. A typical or average strut lengthmay be in the range of from tens of microns to hundreds of microns orthousands of microns. An implant 10 may comprise thousands of struts300, or tens of thousands or more of struts 300. Empty space betweenstruts 300 may, for example be defined by struts 300 that may have anaverage dimension in the hundreds of microns. For example, acharacteristic dimension of a cell (space enclosed by struts that arenear each other) may be in the range of 400 microns to 750 microns. Thethickness of region 200, measured from the external enveloping surfaceto the interface between first region 100 and second region 200, may beapproximately 1 millimeter. The number of cells in that thickness may,on average, be more than one, for example several cells.

Observable in FIGS. 2A-2D is a portion of the external surface that, ona size scale greater than the dimensions of the struts 300, has anexternal enveloping shape that is either flat or curved in a simplecurvature that corresponds to an overall external shape of the implant10. Such an external shape may occupy at least a portion of the externalor bone-facing surface of the implant 10.

Enveloping Shapes that are Axisymmetric

In general, an axisymmetric surface is a surface that could be formed byrevolution of a generatrix curve or shape around an axis of revolution.Shapes that are axisymmetric include spheres, hemispheres, spheroids,ellipsoids, cylinders, cones and frusta of cones. For those shapes, thegenetratrix is either a curve or a line. Other shapes of generatrix thatare more complicated can also be used to produce other surfaces ofrevolution, which are still axisymmetric. In contrast, examples ofshapes that are not axisymmetric include those just-mentioned shapes ifthey contain additional features that occur only at certain angles withrespect to the axis of revolution and do not occur at other angularlocations with respect to the axis of revolution.

Referring now to FIGS. 3A-3B, in an embodiment of the invention, therecould be provided an implant 10 that has an external surface that has anengagement ridge 600 going around the entire circumference of the secondregion 200, which is on the external or bone-facing surface of theimplant 10. The engagement ridge 600, in cross-section, can resemble atooth having a local sharpness. For such a surface, the generatrix wouldbe a curve that includes the tooth or sharpness feature that is visiblein cross-section. If the exterior of the implant 10 is at leastapproximately hemispherical, this engagement ridge 600 may be orientedlike a line of latitude on a spherical globe. The direction of the toothor its local sharpness may point toward the rear of the implant 10, withrespect to the direction of motion for implantation of the implant 10into a surgical site. In the illustrated case of a hemispherical implant10, the direction of the local engagement ridge 600 may point toward theequator of the hemisphere. The engagement ridge 600 and its orientationmay be such that the implant 10 can pass into a bone site more easilythan it can move in the reverse direction exiting the bone site. Theengagement ridge 600 or engagement ridges 600 could have a particularplacement or distribution on the surface of anat-least-approximately-hemispherical implant. With continued analogy toa globe, if the hemisphere is thought of as having an equator and apole, the engagement ridge(s) 600 may exist primarily near the equatoror closer to the equator, and not so much or not at all in the polarregion of implant 10.

The engagement ridge 600 may be made fully or at least partially ofstruts 300. The struts that make up the engagement ridge 600 and secondregion 200, i.e., both the engagement ridge 600, and the generallyhemispherical shape of the remainder of second region 200 that does nothave an engagement ridge 600, may all be part of a continuousinterconnected network of struts 300.

In FIGS. 3A-3B, the engagement ridge 600 is shown as extending entirelyaround the full angular circumference of implant 10, but in a moregeneral situation, a structure resembling engagement ridge 600 might beplaced such that it occupies less than the full angular circumference ofimplant 10. This latter would be an example of an implant design that isnot axisymmetric.

Enveloping Shapes that are Non-Axisymmetric

Referring now to FIGS. 4A-7E, there are shown embodiments of theinvention that are not completely axisymmetric.

An example is the macroscopic surface-interrupting feature, such as fins500, which is illustrated in FIGS. 4A and 4B. FIG. 4B is a sectionalview of FIG. 4A. The fins 500, as illustrated in FIGS. 4A and 4B, may besomewhat step-wise or abrupt in their shape relative to the overallsurface of the implant 10. The fins 500 shown in FIGS. 4A-4B aresufficiently well-defined so that their enveloping shape may exhibitside surfaces and possibly other surfaces that may be at leastapproximately flat. The fins 500 may be made of an array ofinterconnected struts 300, which may be continuous and interconnectedwith, or substantially continuous and interconnected with, the array ofinterconnected struts 300 elsewhere in second region 200 of implant 10.For simplicity of illustration in FIGS. 4A-4B, the struts are not shown.The fins of FIGS. 4A-4B have a cross-sectional shape that is generallyrectangular.

FIGS. 4C-4D also show fins 500, but these fins 500 have across-sectional shape that is generally triangular. FIG. 4D is a bottomview of FIG. 4C. The fins 500 are shown as being made of an array ofinterconnected struts 300, which may be continuous and interconnectedwith, or substantially continuous and interconnected with, the array ofinterconnected struts 300 elsewhere in second region 200 of implant 10.

Referring now to FIGS. 5A and 5B, for an embodiment of the invention,there are shown views of a generally hemispherical exterior surface thatalso has some localized features, which have similarities to the fins ofFIGS. 4A-4D but are less dramatic or abrupt in their overall envelopingshape. Both the generally hemispherical exterior surface and thelocalized features are made of a plurality of interconnected struts.FIG. 5A is an outline of a second region 200 (first region 100 notshown) for a shape such as a generally hemispherical shape that has someadditional features. For clarity of illustration, individual struts arenot shown in FIG. 5A. This outline illustrates both a majority externalsurface shape (generally hemispherical) and a macroscopicsurface-interrupting feature 400, which may be described as resemblingcrests 520, which may be superimposed onto the majority external surfaceshape. As illustrated, in cross-section in FIG. 5A, the majorityexternal surface shape in cross-section is circular, and the macroscopicsurface-interrupting feature 400 is crests 520 or peaks that extendbeyond the circular shape. FIG. 5B shows a possible actual strutconstruction of the second region 200 in which there is illustrated botha majority external surface shape that is a portion of a hemisphere, andmacroscopic surface-interrupting features that are crests 520 or peaks,with all of these features being made of an array of interconnectedstruts 300. It can be considered that what is shown in FIGS. 5A-5B arefeatures that are less abrupt or prominent than the fins 500 of FIGS.4A-4D. For clarity of illustration in FIG. 5B, individual struts areshown but the underlying solid first region 100 is not shown.

As illustrated in FIGS. 5A and 5B, the externally-facing surface ofimplant 10 may comprise a majority external surface shape that occupiesa majority of the envelope of the external surface of second region 200.It is possible that the majority external surface shape may beaxisymmetric and, specifically in this situation, hemispherical. FIG. 5Ais a view of an outline shape, which could be seen by looking at the endof implant 10 that shows the interior of the hemisphere, and for clarityof illustration, individual struts are not shown. FIG. 5B is an externalview, for a shape such as a generally hemispherical shape with someadditional features. FIG. 5B is a view of the second region 200 showingindividual struts both at the exterior and within the region. FIG. 5Bcan be seen by looking at the end of implant 10 that is exterior convex.For clarity of illustration, first region 100, which would be solid, isnot shown in FIG. 5B, nor is it shown in FIG. 5A.

It is illustrated in FIGS. 5A-5B that the externally-facing surface ofimplant 10 may comprise at least one macroscopic surface-interruptingfeature 400 that differs from the majority external envelope shape orthat interrupts some symmetry of the majority external surface shape.Non-limiting examples of such macroscopic surface-interrupting features,which are further described elsewhere herein, include a fin 500, a crest520, sawteeth 550, an engagement ridge 600, and a divertor structure700. Except for an engagement ridge 600, these macroscopicsurface-interrupting features 400 may interrupt the overall axisymmetryof the external surface of implant 10.

An engagement ridge 600, a fin 500, a crest 520, a macroscopicsurface-interrupting feature 400, or any other feature described herein,may serve purposes such as helping to maintain the position of theimplant 10 in bone and resisting motion or change of position of theimplant 10 relative to the bone. Non-limiting examples of motion thatcan be resisted by such macroscopic surface-interrupting features 400include rotation of the implant 10 around its axis of symmetry, orgenerally around any axis, after it has been implanted, andtranslational backing out of the implant 10 along the direction ofimplantation of the implant 10.

The macroscopic surface-interrupting feature 400 may comprise aplurality of interconnected struts 300. If there are a plurality ofmacroscopic surface-interrupting features 400, some of them or all ofthem may comprise a plurality of interconnected struts 300. It ispossible that the entirety of a macroscopic surface-interrupting feature400 may be made of interconnected struts 300, or only a portion ofmacroscopic surface-interrupting feature 400 may be made ofinterconnected struts 300. The array of interconnected struts 300 thatmake up the macroscopic surface-interrupting feature 400 may besubstantially continuous with the array of interconnected struts thatmake up the majority external envelope shape of second region 200. It isdiscussed elsewhere herein that, alternatively, macroscopicsurface-interrupting features 400 could be solid or substantially solid,even if this means interrupting the array of interconnected struts 300.

In FIGS. 5A and 5B, the macroscopic surface-interrupting feature 400 hasan external contour that is somewhat sharp at its externally projectingpeak, while the rest of the fin or feature is more gradually and gentlycurved.

It is possible that at a feature that is sharp, such as the tip ofengagement ridge 600 or a corner of a fin 500 as shown in FIGS. 4A-4B,or a tip of a fin 500 as shown in FIG. 5B, or a tip of a crest 520 asshown in FIG. 5D, the tip of the feature could be a series of struts 300in succession that are at least approximately parallel to each other orin line with each other, thereby forming a sort of a cutting edge. Forexample, in FIG. 5B there is highlighted a place where three consecutivestruts are at a ridge or peak of a crest or a fin, approximately in linewith each other, forming sort of a cutting edge. However, this is notessential.

Yet another possibility is that the external surface of implant 10 mighthave features that are pertinent to anchoring or might benon-axisymmetric, and yet might not be separable into an identifiablydistinct majority external surface shape and an identifiably distinctmacroscopic surface-interrupting feature. For example, around acircumference of the implant 10, with the circumference being taken in asection plane that is generally perpendicular to a direction ofinsertion of the implant 10, the circumference may comprise a sequenceof smoothly or continuously varying peaks and valleys. It might happenthat the general appearance of the exterior resembles a hemisphere andyet there could be surface portions that do not exactly coincide with ahemispherical shape. For example, the enveloping shape other than atpeaks could have, in cross-section, flat panels or segments (asillustrated in FIG. 5C) rather than bidirectionally curved segments thatwould be characteristic of a perfectly hemispherical surface. The peaksmight or might not be identifiably distinct macroscopicsurface-interrupting features, as previously described herein, withrespect to the surface that contains the valleys, i.e, it might or mightnot be possible to identify a distinct point or boundary where themajority external surface shape ceases and the macroscopicsurface-interrupting feature begins, and yet still the surface might benon-axisymmetric in a mathematical sense. FIG. 5D illustrates yetanother such possibility, in which the external shape is composedentirely of curved segments (the individual segments are curved in onedirection of curvature, rather than bidirectionally curved as in atraditional hemisphere). All such possibilities are still considered tobe embodiments of the invention. It is even possible that bothconcavities and convexities could be gently curved. In such instance, across-section of a generally hemispherical implant 10, takenperpendicular to its axis of symmetry, might resemble a circle with asmall sinusoidal variation superimposed on the circle.

The peaks or non-axisymmetric features such as are illustrated in FIGS.4A-5D may be equiangularly spaced around the circumference of theimplant 10, although they do not have to be so spaced. With respect to acenter of the cross-section of the implant 10, the difference in radialposition between a peak and a valley may be at least one typical oraverage length of struts 300. All of the features, or at least some ofthe features, may be made up of struts 300.

Concavities and Convexities

Complex surface shapes, or various of the features referred to herein,may be described in a general way by describing that the externalenveloping surface of implant 10 may have both local concavities andlocal convexities. Again, the external enveloping surface of localconcavities and local convexities may be made of arrays ofinterconnected struts 300. Such arrays of interconnected struts 300 maybe continuous and interconnected with, or substantially continuous andinterconnected with, the array of interconnected struts 300 elsewhere insecond region 200 of implant 10. A concavity may refer, loosely, to adepression in the overall external enveloping surface of the secondregion 200. A convexity may refer, loosely, to a bump or outwardprotrusion in the overall external enveloping surface of the secondregion 200.

For sake of explanation, the presence of both local concavities andlocal convexities may be in contrast, for example, to a simple perfecthemisphere, which may be convex everywhere (bidirectionally convex) inits bone-facing surface. Similarly, the presence of both localconcavities and local convexities would be in contrast in contrast to asimple cylinder or frustoconical surface, which may be convex everywherein its surface such as its surface that would face the internal canalsurface of a medullary canal of a bone. The generally hemisphericalexterior shape is, of course, characteristic of the exterior of anacetabular cup or similar implant, while a generally cylindrical orfrustoconical exterior surface would be characteristic of a stem such asa femoral stem. The presence of both concavities and convexities in sucha surface may help in anchoring the implant 10 to bone, and the presenceof both concavities and convexities could make the external surface ofthe implant 10 sufficiently asymmetric to resist certain kinds ofpossible motion of the implant 10 with respect to the bone, such asrotation.

Concavities and convexities could be smoothly varying having a fairlylarge radius of curvature, or they could be fairly sharp, having a smallradius of curvature. (In the limiting case, a sharp corner would have aradius of curvature of zero). Concavities and convexities could furtherbe a combination of gentle and sharp radii of curvature, such as havinga radius of curvature in one direction that might be gentle and a radiusof curvature in another direction that might be sharp. For example, someof the features of the enveloping surface as shown in FIG. 5A-5B aresmoothly varying. FIGS. 5A and 5B show gentle radii of curvature on theconcavities but a fairly sharp radius of curvature on the convexity. Itwould also be possible, alternatively, for the convexities to have arelatively gentle radius of curvature. Corners, such as right-anglecorners, which are sharp, can be either a convex corner or a concavecorner. The fin 500 shown in FIGS. 4A and 4B has some external cornersthat are fairly sharp and these can be described as convexities also.The same fin 500 has some internal corners that are fairly sharp, andthese can be described as concavities also. Any of these concavities andconvexities can be made of arrays of interconnected struts as describedelsewhere herein, just as the rest of second region 200 can be made ofan array of interconnected struts 300. Non-limiting examples ofconvexities include an engagement ridge, a fin, a fin with teeth, acrest, a peak, and a divertor structure, as discussed elsewhere herein.

Fins

The fin 500 may extend outward relative to a remainder of the majorityexternal surface shape, such as a convex surface, of the implant 10. Afin 500 could be distinct enough that it has identifiable sides, whichmay be at least approximately flat, or parts of it may be more gentle asmight be described by the term crest. Fin 500 may be a shape thatcomprises multiple struts 300. A fin 500 may have a dimension extendingoutward, in comparison to the majority external surface shape, that isat least one typical length of a strut 300.

A specific possible shape of implant 10 is a shape in which the exteriorof the implant 10 may have a mostly hemispherical shape and, in such asituation, the shape may be described, by analogy with Earth'sgeography, as having an equator, a pole, and lines of latitude andlongitude. In such a situation, the fin 500 may have a path thatcorresponds to a line of longitude on the hemisphere. More generally, ifat least some features of the external surface of implant 10 areaxisymmetric around an axis of revolution, the fin 500 may lie generallyin a plane that contains the axis of revolution. However, other shapesand paths of fin 500 are possible also (for example, helical ortwisting).

If there is a plurality of fins 500 or similar features, the fins 500 orpattern of peaks and valleys can be periodic at equiangular intervalsaround the equator. However, such equiangular spacing is not essential.The fin(s) 500 may provide an anti-rotation feature that prevents theimplant 10, when implanted into bone, from rotating, with respect to thebone, around the axis of revolution of its majority external surfaceshape. Fins 500 or similar features may be distributed in a repeatingpattern and may be substantially identical to each other, which mayenable the implant 10 to be repositioned at another position that isdifferent in its angular position around the axis of revolution, ifdesired. For example, there may be approximately 20 such fins 500distributed equiangularly around the circumference or equator of theimplant 10. There could be 40 such fins 500 or features spaced aroundthe circumference, or some other number. Alternatively, if desired, theangular distribution of the fins 500 around the circumference could beother than equiangular.

The fin 500, at its base joining the majority external surface shape,may have a width, in an equatorial direction, that is at least one strut300 wide. At its most outward places, the fin 500 may simply compriseonly a single strut 300 that extends along the long direction of the fin500. This may provide a sharpness, to the extent that a feature made ofdistributed struts 300 can be thought of as having sharpness, which canhelp the fin 500 to cut into bone. Alternatively, the fin 500 could havemultiple strut-lengths even at its tip. The fin 500 may have a height ora dimension extending outward from a remainder of the external or convexsurface of the implant 10, such that this dimension tapers or varies ina desired manner. For example, if the implant 10 is at leastapproximately hemispherical having an equator and a pole, this dimensionmay be greater in a portion of the implant 10 such as close to theequator, and may taper to a smaller dimension at a portion of theimplant 10 such as near the pole. This is illustrated in FIG. 4A, inwhich the fin height may gradually taper or the fin 500 may graduallydisappear upon approaching the pole. Other tapers and configurations offin 500 are also possible if desired.

A leading edge may refer to a portion of a fin 500 or macroscopicsurface-interrupting feature 400 that first encounters bone as theimplant 10 is advanced into an intended position in bone. A trailingedge may refer to an edge that is opposed to a leading edge, along ageneral direction of travel. It is possible that fin 500 could have aleading edge that is sharp. It is possible that the fin 500 could have atrailing edge that is blunt, such as if the fin 500 will be within theregion of natural bone when the implant 10 is in its implanted position,such as if the fin 500 does not extend all the way to the equator of animplant 10 that is hemispherical or nearly hemispherical on its exteriorsurface.

The fin 500 could be made of an array of interconnected struts 300, orat least some of the fin 500 could comprise an array of interconnectedstruts 300.

As yet another possibility, an external enveloping surface could be madeof a plurality of flat segments or a plurality of one-directionallycurved segments such as cylindrical segments. These are illustrated inFIGS. 5C and 5D. In FIGS. 5C and 5D, there is illustrated an implant 10having both a first region 100 and a second region 200, and alongside isillustrated what the implant might look like in the absence of thesecond region 200. FIG. 5D resembles a conventional umbrella in which itcan be appreciated that although the overall shape may approximate ahemisphere, in more detail the surface is defined in curved panels thatare curved in one direction only, thereby being like segments ofindividual cylinders. An enveloping surface as illustrated in eitherFIG. 5C or FIG. 5D could be the enveloping surface of the array ofinterconnected struts that makes up second region 200, just as describedfor other shapes such as engagement ridges and fins. A cylindricalsegment (as in FIG. 5D) would have curvature in one direction, but onlyin one direction. A flat segment or panel (as in FIG. 5C) would have nocurvature in any direction. The shapes illustrated in both FIGS. 5C and5D would have an ability to anchor into bone, such as a preparedhemispherical socket in bone, in a way that prevents or deters orresists rotation of the implant around its longitudinal axis or aroundthe direction of implantation. This may happen in somewhat the same wayas would be accomplished by fins, although with a lessdramatically-varying shape. Both of these shapes (FIGS. 5C and 5D) couldbe implanted in a surgical site in which a surgical preparation toolforms a generally hemispherical socket in bone.

It is possible that the adjacent solid region (first region 100) couldhave generally the same shape as the described enveloping shape.Alternatively, the adjacent first region 100 could have a differentshape, such as for example a simple hemisphere. The shape that has justbeen described in reference to macroscopic surface-interrupting featuresis the external enveloping shape that envelopes the array ofinterconnecting struts 300.

Teeth

In addition to the previously-described basic shape of a fin, andreferring now to FIGS. 6A-6F, a fin sawtooth shape 550 may exist on anoutward-facing surface of a fin 500. The fin sawtooth 550 may existsubstantially all along an outward-facing surface of a fin 500, or itmay exist only in some places, and its dimensions could vary as desired.If the implant 10 is at least approximately hemispherical on itsexterior having a pole and an equator, the fin sawtooth feature 550 mayexist primarily near the equator and might exist not so much or not atall in the polar region of implant 10. The fin sawtooth 550 could bemade of an array of struts 300, or at least some of the fin sawtooth 550could comprise an array of struts 300. The fin sawtooth 550 may have itstip, and may have a width, in an equatorial direction, that is at leastone strut-length of a typical strut 300. The cutting edge of the tip ofa sawtooth 550 could be a single strut 300 or a series of struts 300that are approximately aligned with each other. FIG. 6F illustratesindividual struts 300 making up the second region 200, the fin 500, andthe sawteeth 550 on the fin 500.

As illustrated in FIGS. 6A-6F, fin sawteeth 550 are superimposed ontothe external surface of a fin; however, more generally, such atooth-like structure, either singly or in a series, could besuperimposed onto any shape or portion of the implant 10.

As illustrated in FIGS. 6A-6F, a tooth 550 is essentially triangularwhen viewed from the side of the tooth, i.e., its external shape is madeof straight-line segments. However, it is also possible that some of theshape of the edges or surfaces could be curved or other shape ifdesired. For example, teeth as found in certain animals can have agenerally sharp tip while at the same time having some curvature intheir overall shapes.

If there are successive teeth on a fin, the heights of various teeth,relative to the rest of the local surface, do not have to be constant orequal. Similarly, the distances of the tips of such teeth from areference axis of the implant do to have to be constant or equal,either. For example, there may be a pattern of the heights of successivefins that may continuously vary along a given direction. Such a patternmay resemble the cutting tool known as a broach, in which each toothextends farther out than a preceding tooth by a defined amount. Also, afin with sawteeth could exist on a femoral stem, for example.

Divertor Structure

Reference is now made to FIG. 7A through FIG. 7E. It can be understoodthat if the fins 500 generally lie in respective planes that contain theaxis of the direction of implantation of the implant 10 (such as if thefins 500 lie along lines of longitude using the analogy of the geographyof the Earth, for situations in which the implant 10 is at leastapproximately hemispherical on its exterior), it is possible that thefins 500 could cut corresponding grooves into the natural bone as theimplant 10 is advanced into place in a prepared socket in bone and thefins 500 pass through the bone. It may be considered (although it is notwished to be limited to this explanation) that the material of naturalbone is somewhat malleable, able to be pushed around and reshaped tosome extent by shapes and objects that exert force on the bone oradvance through the bone. If, after implantation, the implant 10 has anytendency to back out, in a direction opposite to the direction ofadvancement during implantation, it is possible that those groovesformed in the bone, which might remain open after the fins 500 havepassed along their insertion path, could possibly provide a pathconducive to the backout motion of implant 10. Such backout motion wouldbe undesirable.

To counteract this possible tendency, there may be provided provideadditional structures on the implant 10, which may be called divertorstructures 700. These divertor structures 700 may be located rearward ofthe fins 500 (with respect to the direction of motion for insertion ofthe implant 10 into bone), such as closer to the equator than the finsthemselves. With respect to equatorial angle, the divertor structures700 may be located between the fins 500 or, more generally, may belocated so that they are not perfectly in line with fins 500 along thepath of the fin 500. The divertor structure 700, when viewed along thelengthwise direction of fin 500, could overlap only partially with fins500, or it might not overlap at all with fins 500. It is possible thatdivertor structure 700 could have a leading edge that is sharp. It ispossible that the divertor structure 700 could have a trailing edge thatis blunt. The location and shape of the divertor structures 700 may besuch as to redirect bone material back into the grooves, in the bone,that the fins 500 have created by the forward motion of the implant 10during its implantation. That rearranged bone material would partiallyblock the groove that was just created by the passage of the fin 500.Such rearrangement of bone material may help to resist possible motionin which the implant 10 might back out if its implanted location bymoving in a direction opposite to the direction of implantation of theimplant 10, although it is not wished to be limited to this explanation.For implant 10 whose exterior is at least approximately a hemisphere,divertor structures 700 may be located close to the equator. It ispossible that the fins 500 could end without extending all the way tothe equator, and the divertor structures 700 could be located closer tothe equator than the ends of the fins 500.

Similarly to other types of macroscopic surface-interrupting features400 described elsewhere herein, the divertor structure 700 may be madeof or can comprise an array of struts 300. The divertor structure 700may have a dimension out of the surface of implant 10 that is at leastone typical or average length of struts 300.

Alternatively it is possible, as illustrated in FIGS. 7A-7E, that adivertor structure 700 could be formed of solid or substantially-solidmaterial like first region 100. Such a solid structure would interruptthe second region 200 of interconnected struts 300, exposing solid orsubstantially solid material to bone in some isolated places. Theexistence of solid or substantially solid material in such places mayprovide mechanical strength to the divertor structure 700. A divertorstructure 700 is not the only localized shape that could be made ofsolid or substantially-solid material amongst or interrupting an arrayof interconnected struts 300. Similarly, fins 500, sawteeth 550, anengagement ridge 600, or generally any desired shape could be made ofsolid or substantially-solid material, even while other nearby portionsof the surface comprise arrays of interconnected struts 300. In additionto acetabular cups, a femoral stem could have such a structure, andgenerally any other shape of implant could have such a structure.

Porosity, Pore Size, Average Strut Dimension, and Empty Volume Fraction

In general, two parameters that can describe a porous structure areporosity and pore size. In general, within any region of any size orshape that may be considered, porosity is the volumetric fractionrepresenting the volume of empty space in the region compared to theoverall volume of the region. Porosity is a fractional number betweenzero and one. For purposes of calculating porosity, in order for thecalculated quantity to have a representative physical meaning, it ispreferable that the region considered should be at least the size of onepore, and preferably, for statistical purposes, should contain aplurality of pores. Nevertheless, the region considered can be smallerthan the entire implant 10; it is entirely possible to describe a localregion by calculating a porosity for a local region that is only aportion of the entire porous region of the implant 10.

Pore size can be considered to be a characteristic dimension thatrepresents or describes the empty space within a pore. If a cell or poreregion is not spherical or symmetric or of uniform dimension, arepresentative pore size may be used that is an average of internaldimensions of a pore taken in multiple different directions, or is adimension of a sphere having an equivalent volume equal to the emptyspace within the pore.

In an embodiment of the invention, for the described array of struts,internal dimension of polygons or polyhedra that make up the array ofstruts 300, as discussed elsewhere herein, may be chosen to be within asize range that is known to be conducive to bone ingrowth. The internaldimensions of polygons or polyhedra, or average lengths of struts, canbe chosen to correspond to a pore size range that is conducive to boneingrowth. The internal dimensions of the polygons may fall within adistribution of sizes. The local empty volume fraction of the regionmade up by interconnected struts can correspond to a porosity range thatis known to be conducive to bone ingrowth. As a numerical example, insecond region 200, the local empty volume fraction may be betweenapproximate values of 30% and 70%. The characteristic dimension of anenclosed cell region formed by struts 300, which roughly corresponds toan average strut length, may range between approximate values of 0.1millimeter and 1 millimeter. The average thickness of second region 200,measured from the interface between first region 100 and second region200, to an external enveloping surface of second region 200, may rangebetween approximate values of 0.5 mm and 1.5 mm.

If the implant 10 is an acetabular cup or has a geometry having anyhemispherical external features, the implant 10 may be described ashaving an equator and a pole. The terms equator and pole are used byanalogy to the geography of the Earth. Equator may correspond at leastapproximately to the equator of a hemisphere, but the interior of theimplant 10 such as an acetabular cup need not be exactly or fully ahemisphere. For example, it is possible that the cup could go fullyaround the axis of revolution while occupying less than a fullhemisphere, but for present discussion the word equator might still beused. More generally, the equator may be a path or band that goessubstantially around a substantially axisymmetric external opening ofthe implant 10. With continuing analogy to the geography of the earth,it is possible that the acetabular cup could be a full hemisphere suchas the northern hemisphere, occupying latitudes from 0 degrees (theequator) to 90 degrees (the north pole). Alternatively it is alsopossible that the acetabular cup could occupy latitudes such as from 10degrees latitude to 90 degrees (the north pole), or as still anotheralternative the acetabular cup could even extend a few degrees beyondthe equator into the southern hemisphere.

It is possible that at the equator, the average strut length (a lineardimension) can be smaller than it is at the pole. It is also possiblethat the local empty volume fraction of the region made up byinterconnected struts (which is a fraction between zero and one) can besmaller at the equator than it is at the pole. Either of these could betrue by itself, or both of them could be true simultaneously. This wouldbe related to the fact that the typical positioning of an acetabular cupimplant in bone is such that the equator of the implant is adjacent tocortical bone, which is relatively more dense and has a relativelysmaller pore size, and the pole of the implant is adjacent to cancellousbone, which is relatively more porous having a relatively larger poresize. If there were a situation where the bone had opposite direction ofhow the porosity or pore size of the bone varied, or if somethingdifferent were desired for any other reason, it would also be possibleto provide the opposite trend of how the local empty volume fraction ofthe region made up by interconnected struts or the average strut lengthof the implant varied from the equator of the implant to the pole of theimplant. The variation of the average strut length or the local emptyvolume fraction of the region made up by interconnected struts or both,in the second region 200, could exist in a stepwise manner. Yet anotherpossibility is that between the equator and the pole of the implant,there can be a continuous variation or gradient of the local emptyvolume fraction of the region made up by interconnected struts, acontinuous variation or gradient of the average strut length, orcontinuous variations or gradients of both of these quantities. It isstill further possible that there could be a continuous variation of oneof those parameters in combination with a stepwise variation of anotherof those parameters. In a device that has an axis of revolution, thedistributions of these local parameters can be axisymmetric, althoughthey do not have to be. The function that describes this variation ofaverage strut length does not have to be the same as the function thatdescribes the variation of local empty volume fraction of the regionmade of interconnected struts. For example, one of these variationscould be linear while the other could be some other function. Thestarting or ending points of these variations could be different.

Yet another possible variation would be to vary the thickness orcross-sectional area or shape of the struts from one place to another inthe implant, to the extent that such variation is permitted orachievable by the manufacturing process.

Any of these described features such as engagement ridges, fins, crests,teeth, macroscopic surface-interrupting features, concavities andconvexities, and divertor structures, could have within them variationsof local average strut length or local empty volume fraction or both asjust discussed for the implant in general. Such variations could bestepwise variations or continuous variations as desired. For example,the variation could be such as to place, in a region of the implant 10that would abut cortical bone, an array of interconnected struts thathas smaller average strut length or smaller local empty volume fractionor both, than in some other part of the implant 10. Similarly, thevariation could be such as to place, in a region of the implant 10 thatwould abut cancellous bone, an array of interconnected struts that haslarger average strut length or larger local empty volume fraction orboth, than in some other part of the implant 10. Such variation could bepresent in the concavities or the convexities or both, or generally inany local feature that may exist in or on the implant 10.

Tapered Struts

In an embodiment of the invention, there may be provided struts whosecross-sectional area varies as a function of position along the lengthof the strut. FIG. 8A-8C show an array of interconnecting struts inwhich, for purposes of illustration only, in one half of theillustration, the struts are of constant cross-section along theirlength, and, in the other half of the illustration, some of the strutsare tapered along their length. In FIG. 8A, as well as in FIG. 8C, thebottom edge of the array of struts is where the struts would connect tothe solid or nearly-solid first region 100. For clarity of illustration,this region 100 is not shown. In FIGS. 8A-8C, the tapered strut islabeled as tapered strut 310. The larger-cross-section end is 311, andthe smaller-cross-section end is 312. In the tapered illustrations inFIGS. 8A-8C, not all of the struts are tapered. The struts close to thesolid or nearly-solid first region 100 are shown as being tapered, whilethe struts further away in that same array are shown as being untapered.

FIG. 8A is a three-dimensional perspective view. In this illustration,the left side of the illustration shows untapered struts, and the rightside shows some tapered struts. For the tapered struts, thelarger-cross-section end 311 of the strut is toward the bottom of theillustration, which is adjacent to the solid or nearly solid firstregion 100.

FIG. 8B is a top view. The untapered situation is in the left half ofthe illustration and the tapered situation is in the right half of theillustration. In the appropriate half of FIG. 8B, the tapered struts 310are in the background of the illustration. The larger-cross-section end311 of the strut would be further to the background than thesmaller-cross-section end 312. The solid or nearly solid first region100, if it were shown, would be even further in the background.

FIG. 8C is a side view. In this illustration, the left side of theillustration shows untapered struts, and the right side shows sometapered struts. For the tapered struts, the larger-cross-section portionof the strut is toward the bottom of the illustration. In these Figures,for clarity of illustration, the solid or nearly solid region is notshown. In FIGS. 8A and 8C, the solid or nearly solid region would be atthe bottom of the illustration. In FIG. 8B, the solid or nearly solidregion would be in the background.

As illustrated, in this situation, the larger-cross-section portion ofthe strut is closer to the solid or nearly-solid region, which is firstregion 100. It is believed, although it is not wished to be limited tothis explanation, that such tapering may provide a sort of transitionfrom the high rigidity of the solid or nearly-solid region (first region100) to the lesser rigidity of the second region 200 (the array ofinterconnected struts 300). The second region 200 has lesser rigidity atleast because of its open space. By virtue of the tapering of some ofthe struts, the change in stiffness is not as sudden as it otherwisewould be, but instead can be more gradual. It is believed, althoughagain it is not wished to be limited to this explanation, that such atransition may improve load transfer between the first region 100, thestruts 300, and eventual ingrown bone. It is believed that this mayimprove on a situation that could be considered to be analogous to astress concentration factor in more classical forms of solid mechanics.As a non-limiting example, the total included angle of taper of atapered strut 310 may be several degrees. Tapering of tapered struts 310may contribute to a gradual change of local empty volume fraction withinsecond region 200.

Cantilevers

As described elsewhere herein, an embodiment of the invention may have asurface-mesh, such that a mesh may approximately conform to a desiredoverall surface shape and may be filled with polygons or surfaces ofpolyhedra formed by struts 300.

In another embodiment of the invention, and referring now to FIGS. 9-12,there may be a surface mesh that approximately conforms to a nominalsurface as just described but, in addition, at at least some of thevertices on the surface, there may be a cantilever 800 extendinggenerally outward away from the implant 10 without connecting further toany other vertex or structure. A cantilever 800 may be considered to bea structure resembling a strut in its dimensions and general appearance,and may be manufactured by the same process as struts. However, incontrast to struts, which would join other struts at both ends of thestrut, a cantilever may be connected to other struts or structure atonly one of its ends. The cantilever 800 may extend out unsupported,from the vertex or structure to which it is connected. The cantilever800 may extend out for a distance that is comparable to or less than thetypical or average length dimension of struts 300 in the mesh. The tipof the cantilever 800 farthest from the implant 10 may be either sharpor blunt to any desired degree. In general, such cantilevers 800 couldbe thought of as resembling the thorns that are found on some plants,the barbs on some fishhooks, or porcupine quills. Shapes and featuressuch as fins, engagement ridges and sawteeth, discussed elsewhereherein, may be on a slightly larger dimensional scale than cantilevers,and may be made of pluralities of struts. However, as discussed herein,it is also possible for features such as fins, engagement ridges andsawteeth to comprise cantilevers on their exteriors.

A cantilever 800 may have a generally lengthwise direction having anorientation. One possibility is that cantilevers 800 could be generallyperpendicular to the local surface. Another possibility is thatcantilevers 800 could be directional extensions of struts that alreadyexist near the surface of implant 10 and that join the same vertex asthose struts. Still another possibility is that the cantilevers 800, orat least some of them such as a majority of them, may point generallyrearward with respect to the direction of motion for the implant 10 tobe advanced into its implantation site in the patient's body. Theoutward-pointing cantilevers 800 can (at least most of them) be angledat an angle similar to each other, not perpendicular to the localsurface and not a simple extension of a mesh, but rather so as toprovide a preferred insertion direction of the implant 10 and so as tohave resistance to reverse motion of the implant 10 in a direction thatis opposite to the preferred insertion or advancement direction ofimplant 10. For the various cantilevers 800, the angles of individualcantilevers 800 could be at a defined angle relative to the axis ofrevolution of the implant 10, or could be parallel to the orientationsof other cantilevers 800, or could be at a defined angle relative to thelocal surface tangent of the implant 10, or could have any other desireddefinition or constraint. For an implant 10 that has an external shapethat is at least approximately hemispherical, it is possible that atleast some, or all, of the cantilevers 800 could point toward theequator. Cantilevers 800 in different locations could point in variousdifferent directions if desired.

Also, as illustrated, for a geometry of an acetabular cup or similargenerally hemispherical shape, it is possible that these cantilevers 800may be provided in regions at or near the equator of the implant 10, butthey may be absent or less common at or near the pole of the implant 10.More generally, it is possible for there to be a greater number ornumber per unit area of cantilevers 800 at or near the equatorialregion, compared to at or near the polar region. In general, cantilevers800 may be placed at substantially all vertices within a local region,or may be placed at less than all of the vertices within a local region.Of course, the dimensions of individual cantilevers 800 can also bevaried as may be desired. A cantilever 800 could be tapered if desired,similarly to struts 300. For example, a cantilever 800 could have alarger cross-section near its joined end and a smaller cross-sectionnear its cantilevered end.

Cantilevers 800 can exist on some portion of the majority surface, orall of the majority surface. The locations in which cantilevers 800 areprovided can be selected by angular position with respect to a polarangle, or by angular position with respect to an azimuthal angle, or bysome combination of polar angle and azimuthal angle.

It is believed, although it is not wished to be limited to thisexplanation, that such cantilevers 800 may improve initial mechanicalfixation of the implant in its intended implantation site, especially atand shortly after the time of surgery, before bone ingrowth and healinghas occurred.

Such cantilevers 800 may also be used for other shapes of implants otherthan the illustrated generally hemispherical implant. For example, suchcantilevers 800 may be placed on a stem such as a femoral stem, or ingeneral any stem that is intended to go into a canal of a long bone.Cantilevers 800 may be placed on a flat surface, or on a curved surfaceof any curvature. In any such usage, cantilevers 800 may be placed wherethe surface tangent of the external surface of the implant 10 isapproximately parallel to or is at a shallow angle relative to thedirection of motion for implantation, and cantilevers may be absentwhere the local surface tangent of the external surface of the implant10 is relatively closer to perpendicular to the direction of motion ofthe implant 10 for implantation. It is believed, although it is notwished to be limited to this explanation, that cantilevers where thesurface tangent is approximately parallel to or is at a shallow anglerelative to the direction of motion for implantation are better able todig into the bone to resist backing-out of the implant becausebacking-out motion would cause them to dig into bone such as to resistfurther backing-out.

Cantilevers 800 can be on a macroscopic surface-interrupting feature400, although they do not have to be. For example, cantilevers 800 maybe placed on a macroscopic surface-interrupting feature such as a fin500. Cantilevers 800 might be placed on some portion or surface of amacroscopic surface-interrupting feature 400 while being absent fromsome other portion or surface of the macroscopic surface-interruptingfeature 400. Placement can be on a side surface while being absent on aradially-facing surface, or vice versa, or can be on some portion ofsawteeth 550 while being absent from other portions of sawteeth 550.Cantilevers 800 can be placed on the peaks of a peak-and-valley type ofsurface such as is discussed elsewhere herein. Of course, cantileverscan also be placed on the majority external surface shape. Cantileverscould be placed on substantially all of the surface vertices in a localregion, or at fewer than all of the surface vertices.

FIG. 10A shows an external view of an acetabular cup, sectioned, showinga first region 100 and also showing a second region 200 that containsinterconnected struts. FIG. 10A also shows, visible especially againstthe background of the illustration, cantilevers 800. Although some ofthe cantilevers 800 in FIG. 10A appear to be perpendicular to the localexternal surface (i.e., parallel to the local normal vector), it is alsopossible that some or all of the cantilevers could be pointed inspecific directions as discussed herein. FIG. 10B, using a much coarserschematic of the network of interconnected struts, shows that thecantilevers 800 can be angled so that they point rearward with respectto the direction of motion for implantation of the implant. FIG. 10Balso illustrates placement of the cantilevers 800 preferentially nearthe equator of the approximately hemispherical external shape of theimplant. FIG. 10B is only a schematic illustration in the sense that thenumber of struts is far fewer than would be found on an actual implant10. FIG. 11 shows fins or crests, similar to FIG. 5B, but cantilevers800 are additionally shown. The cantilevers 800 on the fins 500 orcrests could be pointed in any desired direction, as discussed hereinwith respect to cantilevers 800 in general. FIG. 12 shows a sawtoothfeature similar to FIG. 6, but cantilevers 800 are additionally shown.The cantilevers on the sawteeth could be pointed in any desireddirection, as discussed herein with respect to cantilevers in general.It is possible that the overall external shape of sawteeth could bedefined by an enveloping shape of cantilevers 800. It is possible thatthe overall external shape of features such as convexities, fins, teeth,crests, an engagement ridge, or any other feature could be defined by anenveloping shape of cantilevers 800.

Making a Designed Shape Out of the Envelope of the Cantilevers

Embodiments of the invention have described herein containing an arrayof interconnected struts such that an envelope of the array ofinterconnected struts forms a desired macroscopic shape. However, thereis also another possibility for forming an enveloping shape.

In embodiments of the invention, it is possible that cantilevers 800 canbe located and designed such that an envelope of the tips of thecantilevers forms a desired macroscopic shape. It is possible thatvarious different cantilevers have different lengths, or differentorientations, or both. Such variation can result in an enveloping shapethat is defined by the tips of the cantilevers. Such variation can bedesigned into the implant by virtue of the programmed nature of thepositional definition of the position of each strut 300 and cantilever800.

Referring now to FIG. 12, there is illustrated a situation in which thetips of the cantilevers have an external envelope that has the shape ofa sawtooth. More generally, any desired enveloping shape could becreated. It is possible that the underlying array of interconnectedstruts could have a shape that is roughly similar to the envelopingshape of the tips of the cantilevers. Alternatively, the underlyingarray of interconnected struts need not have any particular relation tothe enveloping shape of the tips of the cantilevers.

Distribution of Locations and Orientations of Cantilevers

In general, a cantilever 800 has two ends, i.e., a joined end and acantilevered end. The joined end is where the cantilever 800 joinssomething else such as a vertex of other struts 300 or alternatively asolid region 100. The cantilevered end simply ends without being joinedto anything else. A cantilever 800 may also be described by itsorientation. The orientation of the cantilever 800 is the orientation ofthe line connecting the joined end to the cantilevered end.

In embodiments of the invention, it is possible that the location of thejoined end may be distributed with some randomness, while theorientations of the cantilevers either may have some randomness or maybe non-random. Alternatively, it is possible that the location of thejoined end may be distributed in a non-random pattern, while theorientations (angular direction) of the cantilevers 800 either may havesome randomness or may be non-random. The lengths of cantilevers couldbe random or could be designed.

Cantilevers that Directly to Join Solid Region

Cantilevers 800 have been discussed herein as being connected to avertex where a plurality of struts 300 come together at a vertex.

Alternatively, in an embodiment of the invention, there may be providedan implant 10 such as an acetabular cup that has a first region 100 ofsolid or substantially solid material that appears on its externalsurface of the implant 10, to which are connected a plurality ofcantilevers 800 projecting from the first region 100 of substantiallysolid material.

In an embodiment of the invention, an acetabular cup may have a band ofsubstantially solid material on its external surface adjacent to acorner or edge. In such an acetabular cup, such a band may be adjacentto the equator of the acetabular cup. For example, such an feature maybe provided based on the expectation that the edge of the acetabular cupnot only might interface with adjacent bone of the acetabulum, but alsomight be slightly exposed to or adjacent to other types of tissue, whichcould be soft tissue that could possibly be irritated by irregularitiesat the edge of the implant. Accordingly, such band may be devoid of theinterconnected struts 300 that are described and illustrated elsewhereherein. However, in this embodiment of the invention, referring now toFIGS. 13A-13C, there may be provided an implant that comprises asubstantially solid region to which are connected a plurality ofcantilevers projecting from a portion of the band.

The cantilevers 800 could join the substantially solid region 100, suchas the solid band, at locations that are distributed with some degree ofrandomness. The distribution and the randomness may be as describedelsewhere herein. Alternatively, the orientation of the cantileverswhere they join the substantially solid region may be random or may havea pattern. In FIG. 13A, such cantilevers 800 are shown projecting onlyup to the edge of the second region 200 that also containsinterconnected struts 300. In FIG. 13B, such cantilevers 800 are shownprojecting from the solid band of region 100 in a row that remains somedistance away from the equatorial edge of the acetabular cup. In FIG.13C, such cantilevers 800 are shown projecting from most of the region100 solid band of the acetabular cup.

In FIGS. 13A-13C, the cantilevers are shown as projecting approximatelyperpendicular to the equatorial band, but of course they could projectat any desired angle.

Cantilevers that are non-straight, such as bent

In an embodiment of the invention, there may be provided cantileversthat are not completely straight. For example, such a cantilever couldbe curved, or such a cantilever may comprise a first straight segmentfollowed by a second straight segment that is not aligned with the firststraight segment. Such two-straight-segment cantilevers 820 areillustrated in FIG. 14.

Such a two-straight-segment cantilever could be described as having avertex that is formed by the junction of only two struts. Such a vertexmay occur only on the outside of the second region 200, i.e., away fromthe first region 100 that is solid or substantially solid. As with otherdescribed cantilevers, such cantilevers 820 may be bone-facing. Suchcantilevers can extend in random directions, or can extend backwardly.Such cantilevers could be present in some zone of the second region 200and absent in another zone of the second region 200. Such cantileverscould have lengths that are random, or else have a designed pattern.Such cantilevers could have ends that form a desired enveloping shape.

Cantilevers of the non-straight variety can be oriented radiallyoutward, or could be oriented in a particular orientation, or orientedin a particular plane, or could be oriented with some amount ofrandomness. The overall lengths of these non-straight cantilevers couldbe uniformed, or random, or patterned according to an algorithm. Suchcantilevers could be provided in some places and not in other places.

Loop Structure

In an embodiment of the invention, there may be provided a structurethat forms a loop structure 900. The term loop structure is used hereinto refer to a non-straight element that is joined at one end to someother structure and joined at another end to some other structure. Theloop structure 900 may be curved or may comprise a series ofstraight-line segments. Such a loop structure 900 is illustrated in FIG.15. It could be described as having a vertex that has only two strutsconnecting at such a vertex.

In an embodiment of the invention that comprises a network ofinterconnected struts, the loop structure 900 may be provided only at asurface of the implant rather than amongst the network of interconnectedstruts 300 in the interior of the network. Such a surface that has loopstructures 900 may, for example, be intended to be bone-facing. It wouldalso be possible to provide loop structures that attach directly to asolid or nearly-solid structure such as first region 100. Propertiessuch as orientations and lengths of loop structures could be uniform,random, or patterned. Loop structures could be provided in some placesand not in other places.

Surgical Tooling and Interference

In an embodiment of the invention, it is possible that the dimensions ofan implant 10 and the dimensions of surgical preparation tooling such asreamers could be coordinated such that there is an intentional mismatchbetween the dimensions of the preparation tool (reamer) and thedimensions of the implant 10, resulting in an interference fit of theimplant in the prepared bone. Further, in connection with this, thesurface of the implant 10 that faces the bone and experiences theinterference fit could be an array of interconnected struts 300. It isfurther possible that there could be cantilevers 800 or loop structures900 or both on the surface or a portion of the surface that is involvedin the interference fit, as described elsewhere herein.

Other Shapes of Implant

Referring now to FIGS. 16-17D, there is shown the possible use offeatures mentioned herein with implants that may have a generally longshape rather than a hemispherical or nearly-hemispherical shape. Theseillustrations show portions of a shape that is elongated andfrustoconical with a gentle taper. FIG. 16 shows an implant having anengagement ridge. FIG. 17A shows an implant having a fin. FIG. 17Billustrates an implant similar to that of FIG. 17A, but showing thearray of struts. FIG. 17C shows an implant having cantilevers. In theseillustrations, only a few instances of respective features are shown,for clarity of illustration. Only a portion of the length of the stem isshown, for clarity of illustration. The stem is shown as beingfrustoconical with a slight taper, but other shapes or tapers are alsopossible. Of course, any of these features could be used together withany others, in any combination. Such a shape could be a stem that issuitable to fit into the intramedullary canal of the femur for use in ahip replacement, or generally could be made such as to fit into theintramedullary canal of any long bone. For example, the device couldalternatively be an intramedullary rod or intramedullary nail such ascan be used for fracture fixation. The device could be at leastpartially cylindrical instead of the illustrated frustoconical shape, orcould be still other shapes.

It can be appreciated that features described herein may be designed andmanufactured into or onto generally any type of implant, such as anytype of bone-facing implant. For an implant that receives a sphericalcomponent, the outside or bone-facing surface of the implant may begenerally convex, and the external convex surface of the implant mayhave any of such features alone or in combination. In general, thefeatures can be on an implant that is inserted into a bone site in atranslational motion, or that is inserted into bone in a rotationalmotion, or that is inserted into bone in a motion that is a combinationof translation and rotation such as a helical (screwing) motion.

Splines and Mesh on a Stem

Sometimes the stems of femoral implants have had longitudinal featuresresembling splines, suitable to engage with bone of the femur so as toresist rotation of the femoral stem around the principal axis of thefemoral stem. In an embodiment of the invention, there may be provided afemoral component that has a stem that has a solid or substantiallysolid central region and has a region of an array of interconnectedstruts adjoining the solid or substantially solid central region.Furthermore, in an embodiment, the region of the array of interconnectedstruts could have an envelope that has a variation of shape as afunction of position on a perimeter of the femoral stem. The variationcould be periodic although it does not have to be. The envelope shapecould have features that continue in a similar fashion at leastapproximately aligned with the long direction of the stem. The shapecould resemble a spline. Such variation could be provided anywhere alongthe long direction of the stem; it could be present in some places andnot in other places. This is illustrated in FIG. 17B. As a possibledimension, the envelope of the spline might have a variation that is 1mm in dimension maximum excursion relative to what would be anenveloping surface without the extending-out feature resembling aspline. The femoral stem might be tapered, such as with a total includedangle of about 3 degrees. As is illustrated in FIG. 17C, the solidregion may have a shape that is not splined, although alternatively ifdesired the solid region could have a shape that is splined. It is notnecessary that any portion of the stem have a circular cross-section.The underlying solid region could have a similar shape similar to theshape of the splines or it need not have any particular relation to theshape of the splined region.

Variation of Properties of Network of Struts

In general, a femoral stem such as for a hip replacement may have across-section that is elongated, especially near the end of the femurthat is close to the hip ball. This means that some parts of theperimeter of the femoral stem are adjacent to bone that is more cortical(relatively more dense, relatively smaller pore size) and other parts ofthe perimeter are adjacent to bone that is more cancellous (relativelyless dense, relatively larger pore size). In an embodiment of theinvention, a stem, such as a femoral stem of a hip implant, may comprisean array of interconnected struts such that the array of interconnectedstruts has different properties at some portion of the perimetercompared to another portion of the perimeter.

For example, referring now to FIGS. 18A-18B, at some place along such astem, the entire perimeter or at least a portion of the perimeter maycomprise interconnected struts. The stem is illustrated as beingelongated in its cross-sectional shape having a longer direction in itscross-section and a shorter direction in its cross-section. At a placeon the perimeter in the middle of a longer direction of the stem, thearray of interconnected struts may have a relatively larger voidfraction or larger average strut length or both. Conversely, at otherportions on the perimeter of the stem, the array of interconnectedstruts may have a relatively smaller void fraction or a relativelysmaller average strut length or both.

It is furthermore possible that the just-described array ofinterconnected struts may further have cantilevers attached to it atdesired places.

Concave Implant

Embodiments of the invention such as are illustrated so far have had abone-interfacing surface whose overall shape has been generally convex.Such implants have been intended to be implanted into a boneconfiguration that is generally concave. In yet another embodiment ofthe invention, referring now to FIG. 19, an implant can be made havingfeatures as described herein, but with an intended bone-facing surfaceof the implant being generally concave and suitable to adjoin or engagewith a bone surface that is generally convex. In such an implant, thefirst region 1910, which may be solid or nearly solid similar topreviously described first region 100, may be located generally on anexterior surface of the implant. The second region 1920, which may be acollection of struts similar to the previously described second region200, may be located generally on an interior surface of the implant.

Furthermore, such a concave surface may also comprise cantilevers asdescribed elsewhere herein in other embodiments. Such cantilevers may beconnected either to an array of interconnected struts or to a solidregion, or both.

For example, an implant of this type might be an implant for resurfacingan articulating joint, as illustrated in FIG. 19. The implant that isillustrated in FIG. 19 would be suitable for resurfacing the end of thefemur that articulates in the knee joint.

Instrument, Such as a Rasp

Implants are not the only type of medical product that can bemanufactured having features as described herein. In an embodiment ofthe invention, there may be provided an instrument having a structuresuch as a substantially solid region 2010 and a region 2020, adjacent tothe substantially solid region, having an array of interconnectedstruts. Such an instrument could be a rasp such as for the purpose ofpreparing bone at a surgical site. Referring now to FIGS. 20A, 20B, 20C,there is illustrated a rasp 2000 that might be used to prepare theintramedullary canal of the femur near the hip, during a hiparthroplasty procedure. Of course, other shapes of rasps or tools,comprising some of the same features, could be made used for otheranatomical sites and other surgical procedures. The illustrated rasp2000 may have an external enveloping shape that may roughly correspondto a shape of a femoral stem. It may have dimensions that are slightlysmaller than respective dimensions of a corresponding femoral stem.There may be provided a handle portion 2090 and a plurality of raspportions 2000, with the rasp portions 2000 being attachable to thehandle portion 2090 and being interchangeable.

Terminal Adapter and Acetabular Cup Having a Smooth Polar Region

An acetabular cup may have a central axis of symmetry. Typically anacetabular cup has an internal feature that is suitable to engage withan instrument. For example, the internal feature may comprise aninternal thread, and the instrument may have a complementary threadedfeature that engages the internal thread. In such a situation, theinstrument can be affixed to the acetabular cup and can be used tointroduce the implant to the surgical site in a patient's body using agenerally translational motion along a direction of motion. In such asituation, the central axis of symmetry of the acetabular cup may atleast approximately coincide with the direction of motion forintroducing the acetabular cup into the surgical site. In such asituation, the surgical incision either may be made, or at least may beable to be stretched, so that the perimeter of the incision isapproximately at least the perimeter of the acetabular cup at itsequator.

However, the just-described orientation for insertion is not the onlypossible orientation with which the acetabular cup could pass throughthe surgical incision. Another embodiment of the invention is aninstrument for use with an acetabular cup for the purpose of providing adifferent orientation of introduction of the acetabular cup through theincision.

It can be realized that the profile of the acetabular cup when viewedfrom the side is approximately a “D” shape. In an embodiment of theinvention, it would be possible to introduce the acetabular cup throughthe surgical incision in a sideways orientation. In such a situation,the surgical incision would have to be made, or at least would have tobe able to be stretched, so that the perimeter of the incision is atleast approximately the perimeter of the “D” shape of the acetabularcup. The perimeter of the “D” shape would be shorter than the perimeterof the acetabular cup at its equator. This could reduce the requiredsize of the surgical incision.

Referring now to FIGS. 21A-21F, there is illustrated an acetabular cup2100 and there is illustrated a terminal adapter 2150. The acetabularcup may have an interface feature such as internal thread. The terminaladapter 2150 may have a corresponding external thread that can engagethe internal thread of the acetabular cup 2100. Elsewhere on theterminal adapter, the terminal adapter 2150 may have an interfacefeature that can engage releasably with an instrument 2170 that has along direction. The respective orientations may be such that the centralaxis of symmetry of the acetabular cup may be approximatelyperpendicular to the long direction of the instrument.

Further in connection with such a surgical procedure, it may be realizedthat if acetabular cup passes through a close-fitting incision while ina sideways orientation, there is the possibility of roughness on theacetabular cup scratching or irritating soft tissue such as at theboundary of the incision. It may further be realized that roughness atthe mid-latitudes and near the equator is quite useful for bone ingrowthand for enhancing attachment to bone, but roughness near the pole of theacetabular cup is less useful for attachment. Accordingly, in anembodiment of the invention, the region near the north pole of anacetabular cup may be manufactured to be completely smooth or at leastmore smooth than other portions of the exterior of the acetabular cup.Such smoothness also avoids filing up spaces with skin tissue.

Also relevant to these considerations, it is even possible that duringsurgery an acetabular cup is brought into the surgical site and is triedand is found to be loose-fitting, and therefore it is decided to removethat cup and replace it with a different, larger cup. This possibilityis an additional reason to want to minimize irritation of the softtissue caused by passage of the acetabular cup through the incision.

The interface between the acetabular cup and the terminal adapter (ifused) and the instrument may be such as to be rotationally rigid, withrespect to at least one direction of rotation. This could allow thesurgeon to rotate or wiggle the acetabular cup somewhat, such as forexample, to scratch the bone prior to final seating of the implant.

An embodiment of the invention may comprise a surgical method in whichan acetabular cup together with a terminal adapter may be insertedthrough a surgical incision in a generally sideways orientation with theterminal already engaged with the acetabular cup. Then, after theacetabular cup has passed through the surgical incision, the instrumentmay be engaged with the terminal piece. The instrument may then be usedto urge the acetabular cup into position in bone.

Potential Uses of Embodiments of the Invention

Embodiments of the invention can be used with generally any joint oranatomical part that involves an implant that interfaces with bone orsimilar tissue.

As discussed herein, embodiments of the invention may be used for anyportion of a hip replacement, such as the femoral component or theacetabular component, or for a resurfacing of any portion of the hipjoint. Embodiments of the invention may be used for any portion of aknee replacement, such as the knee tibial component or the knee femoralcomponent, or for a resurfacing of any portion of the knee. Embodimentsof the invention may be used for any portion of an ankle replacement,such as the talus component or the tibial component, or for aresurfacing of any portion of the ankle.

Embodiments of the invention may be used for any portion of a shoulderreplacement, such as the humeral component or the glenoid component, orfor a resurfacing of any portion of the shoulder joint. Embodiments ofthe invention may be used for any portion of an elbow replacement, suchas the humeral component or the ulnar component, or for a resurfacing ofany portion of the elbow. Embodiments of the invention may be used forany portion of a wrist replacement or for a resurfacing of any portionof the wrist.

Embodiments of the invention may be used anywhere in the foot or thehand. Embodiments of the invention may be used for any hemiarthroplastyor total arthroplasty of a small joint.

Embodiments of the invention may be used as augments such as kneeaugments (e.g. cones, wedges), acetabular augments or other augments.Embodiments of the invention may be used as a replacement of a portionof the patella. Embodiments of the invention may be used as a wedge foran osteotomy, such as for an Evans/Cotton osteotomy or any other type ofosteotomy. Embodiments of the invention may be used as an intramedullarynail. Embodiments of the invention may be used for oncologicreconstructive devices (e.g. replacement of the distal femur, orreplacement of a portion of the humerus). Embodiments of the inventionmay be used for craniomaxillofacial applications.

Embodiments of the invention may be used in a spinal interbody devicesuch as a cage.

Details of Mesh

Referring now to FIG. 2D, it is possible that three or more struts 300may meet at a vertex, especially with some of the tessellation schemesas are described elsewhere herein.

A sequential series of struts 300 may form a polygon. Although thetraditional mathematical definition of a polygon is a shape thatoccupies a plane, for present purposes, it may be considered that apolygon refers to a series of struts that forms a closed shape thateither is planar or is almost planar. A polygon may be referred to as ann-gon, m-gon, o-gon, etc., with the variable n, m, o, etc. referring tothe number of sides that the polygon possesses. A group of adjacentpolygons may form a three-dimensional shape that is a polyhedron.

In an embodiment of the invention, the locations of the struts 300 mayform a pattern that is non-repeating, i.e., does not repeat itselfgeometrically identically anywhere else in or on the implant 10. Theremay be some degree of randomness in the predetermined choice of thelocations and geometry of the struts 300. The randomness may be as aresult of a particular mesh generation scheme or algorithm as describedelsewhere herein, although it is not wished to be limited to anyparticular mesh generation scheme or algorithm. Although it is notwished to be limited to this explanation, it is possible that the use ofmeshes that are non-repeating or even random may appropriately mimic thegeometry and situation that naturally exists in living bone, withbeneficial physiological and clinical results. It is to be appreciatedthat although the pattern of struts 300 may contain some degree ofrandomness and non-periodicity, that pattern is predetermined and isprecisely manufactured and can be so manufactured as many times as maybe desired, thereby producing multiple finished articles that arevirtually identical to each other even at the level of detail ofdimensions and arrangements of struts. In an implant the quantity ofstruts may number in the thousands or even more.

In an embodiment of the invention, the defined non-repeating nature ofthe array of struts 300 may manifest itself such that within a nearbyregion to any particular strut 300, there is no other strut that hasexactly the same length as that particular strut 300. “Nearby” can beconsidered to be the entire implant, or it can be considered to bewithin a specified number, such as five, of strut-lengths away from thereferenced strut.

In an embodiment of the invention, the defined non-repeating nature ofthe array of struts 300 may manifest itself such that within a nearbyregion to any particular strut, there is no other strut that is parallelto that particular strut 300.

In an embodiment of the invention, the defined non-repeating nature ofthe array of struts 300 may manifest itself such that within a nearbyregion to any particular strut 300, there is no other strut that hasexactly the same spatial orientation as a particular strut 300.

A vertex included angle may be considered to be the angle made by therespective centerlines of two struts 300 at their joint at a vertex,assuming that the centerlines of the two struts 300 are eachsubstantially straight segments. In an embodiment of the invention, thedefined non-repeating nature of the array of struts 300 may manifestitself such that within a nearby region to any particular pair of struts300 that join at a vertex, there is no other pair of struts 300 that hasexactly the same included angle as that particular pair of struts 300.

In an embodiment of the invention, the defined non-repeating nature ofthe array of struts 300 may manifest itself such that there may be avertex that is simultaneously a vertex of an n-gon and a vertex of anm-gon, wherein n and m are different integers. It is further possiblethat there may be a vertex that is simultaneously a vertex of an n-gonand a vertex of an m-gon and a vertex of an o-gon, wherein n and m and oare different integers.

In an embodiment of the invention, the defined non-repeating nature ofthe array of struts 300 may manifest itself such that there may be astrut 300 that is simultaneously a side of an n-gon and a side of anm-gon, wherein n and m are different integers. It is further possiblethat there may be a strut 300 that is simultaneously a side of an n-gonand a side of an m-gon and a side of an o-gon, wherein n and m and o aredifferent integers.

In an embodiment of the invention, there may be surface polygons thatgenerally lie on the external surface of the implant 10 and help definethe external surface of the implant 10. In an embodiment of theinvention, there may be non-surface polygons that generally do not lieentirely on the external surface of the implant 10, although they mayhave a side that is on the external surface of the implant 10. Theoverall mesh can include a mesh of surface polygons and additionallycould have layers of non-surface polygons going deeper into the implant10 before meeting the solid region 100. For example, there may be two orthree or more such layers of polygons in the direction going from thesurface into the interior of the mesh. However, it is to be understoodthat there might not be a precise definition of a layer because thevarious polygons may vary in their respective dimensions, numbers ofsides, orientations, etc.

The mesh or array of struts could be such that the number of sidespossessed by particular polygons is not identical for all polygons. Forexample, such a mesh may contain a polygon that is a triangle, aquadrilateral, a pentagon, a hexagon, or a polygon having an even largernumbers of sides. The number of sides could be as large as 8 or 9 oreven more. It is further possible that the mesh could contain one kindof polygon, or two kinds of polygons, or three kinds of polygons, oreven more than three kinds of polygons. Specifically, the mesh couldcomprise at least two different kinds of polygons or at least threedifferent kinds of polygons, each kind of polygon having a differentnumber of sides.

As an example of a mesh comprising only two different kinds of polygons,a mesh could contain at least one triangle and at least onequadrilateral. A mesh could contain at least one quadrilateral and atleast one pentagon. A mesh could contain at least one pentagon and atleast one hexagon.

It is further possible that there could be a mesh of greater complexitycomprising three different kinds of polygons. For example, a mesh couldcontain at least one triangle and at least one quadrilateral and atleast one pentagon. A mesh could contain at least one quadrilateral andat least one pentagon and at least one hexagon. A mesh could contain atleast one pentagon and at least one hexagon and at least one heptagon. Amesh could contain at least one triangle and at least one pentagon andat least one hexagon. Other combinations of kinds of polygons are alsopossible.

As an example of still greater complexity, it is possible that a meshcould contain at least four different kinds of polygons.

There can be a distribution of the quantity of the polygons havingvarious numbers of sides. For example, polygons whose number of sides isin the middle of the range of number of sides could be more common thanpolygons whose number of sides is at the extremes of the range of numberof sides.

With regard to the surface polygons (i.e., polygons that are at theexternal surface of the mesh), the mesh of surface polygons may includepolygons of at least two different side-numbers or at least threedifferent side-numbers.

With regard to non-surface polygons (i.e., polygons located moreinteriorly), these polygons may include polygons of at least twodifferent side-numbers or at least three different side-numbers.

With regard to all polygons, the complete set of these polygons mayinclude polygons of at least two different side-numbers or at leastthree different side-numbers.

With regard to a 3-D mesh or tessellation, such a mesh may be made ofpolyhedra, and polyhedra may be described by the number of surfaces thatmake up the polyhedra. It is possible that the various polyhedra in amesh do not all have to possess identical numbers of surfaces. The meshmay be described by the fact that the mesh can contain polyhedra of twodifferent surface-numbers, three different surface-numbers, fourdifferent surface-numbers or even more different surface-numbers.

Method of Creating Mesh Geometry

In an embodiment of the invention, a mesh may be produced using aVoronoi mesh generation or tessellation method. Voronoi generationschemes are sometimes used for generating mathematical meshes for use inFinite Element Analysis, for analysis of experimental data, for computergraphics, and for other purposes. A Voronoi generation scheme can beused to produce a two-dimensional mesh or a three-dimensional mesh. In atwo-dimensional mesh, the cells are polygons. In a three-dimensionalmesh, the cells are polyhedra. A random number generator is used for aportion of the generation scheme. As a result, the mesh usually containslocal lack of periodicity or lack of a repeating pattern.

Such a generation scheme starts with distributing “seeds” in a region ofspace using a random number generator. There may be some overallconstraints imposed on the distribution of seeds. For example, theoverall number of seeds generated may be constrained, as a way ofconstraining the average density of the resulting mesh. Another exampleof a constraint may be to locate the seeds more than a certain minimumdistance away from each other. In instances in which the constraint isnot met, seeds may be eliminated or relocated or regenerated.

After the locating of the seeds, all points may be categorized intocells according to which seed they are closest to. If the criterion isthe simple criterion of distance to the nearest seed, a cell is thelocus of points that are closer to a given seed than they are to anyother seed. Boundaries between cells are loci of points that areequidistant from two seeds. Vertices are intersections betweenboundaries, and so vertices are points that are equidistant from three(or more) seeds. In a two-dimensional (planar) tessellation, cells areconvex polygons. In a three-dimensional tessellation, the cells arepolyhedra having a number of faces. Another possibility is that insteadof a simple criterion of the boundaries being equidistant from seeds asjust described, the calculation could be performed using weightingalgorithms or more complicated formulas than what was just described.

A 2-D Voronoi tessellation is illustrated in FIG. 22A. In a 2-Dtessellation, the number of sides possessed by the polygons is notfixed, so a particular tesselation can contain quadrilaterals, pentagonsand other kinds of polygons. In a 3-D tessellation, the numbers of facesof the polyhedra can vary, similar to the way the numbers of sides ofpolygons can vary in a 2-D tessellation. FIG. 22B illustrates across-section of a 3-D Voronoi tessellation. In general, a cross sectionof a 3D Voronoi tessellation is not a 2D Voronoi tessellation itself.

In an embodiment of the invention, a Voronoi generation method may beused to generate a uniquely determined geometry of interconnectedstruts, and that uniquely determined geometry of struts is thenmanufactured to form an implant 10.

A two-dimensional Voronoi tessellation can be mapped or wrapped onto athree-dimensional surface. For example, such a mesh could bemathematically stretched or modified in local places as desired.Alternatively, a three-dimensional Voronoi tessellation can be generatedso as to fit within a prescribed three-dimensional shape. It is possiblethat the surface of the mesh can be made substantially entirely ofpolygons of struts, such that the polygons are planar or almost planar,and the interior of the meshed region can have struts oriented generallyin all directions.

An array of struts 300 can have on its surface a mesh of polygons thatat least approximately corresponds to a desired surface shape, andfurther can have additional struts 300 extending internally to form athree-dimensional mesh.

Method of Manufacture

The implant 10 may be manufactured according to a pre-determined,reproducible geometric pattern. Such pattern may include sufficientdetail to define the location, orientation and dimensions of eachindividual strut 300 in the entire implant 10. Using such a method, itis possible to build any number of implants 10 that are substantiallyidentical to each other, within manufacturing tolerances. In particular,the array of struts 300 and the mesh pattern may be substantiallyidentical among various implants 10 built from the pre-determineddescription, within manufacturing tolerances.

In an embodiment of the invention, the implant 10 may be manufactured byan additive manufacturing process. Such a process may be alayer-by-layer additive manufacturing process. In such a process, alayer of powder may be deposited on a working surface. Then, energy maybe deposited in appropriate places on the layer of powder appropriatelyto soften or melt the powder in localized places, appropriately to causethe softened or melted powder to adhere to or fuse with other powderparticles or with already-solidified material in previously-depositedlayers. The softening or melting may be followed by resolidification.Then, another layer of powder may be deposited and the process may berepeated. For production of a device made of metal, the powder maycomprise particles of the appropriate metal. Such metal may, forexample, be titanium or a titanium alloy. The energy deposition maycomprise an electron beam or a laser beam, for example. Production usingan electron beam may be referred to as electron beam melting. In orderto deter possible undesired chemical reactions during the manufacturingprocess, such process may take place in a vacuum, or in an inertatmosphere. For example, the environment in which such process takesplace may be controlled to have an appropriately low concentration ofoxygen. The geometric locations and patterns of energy deposition may besuch as to create a desired three-dimensional shape. Operation of themanufacturing process may be controlled by a computer. Equipment andservices for such manufacturing are available, for example, from ArcamAB (Mölndal, Sweden) and DiSanto Technology, Shelton, Conn. Other typesof additive manufacturing may also be possible.

After completion of the described steps, unbound powder may be removedand any other desired post-processing may be performed. Post-processingcould include conventional machining, surface treatment, chemicaltreatment, or any other desired steps. The product also may be renderedsterile through any appropriate sterilization method, such as gammairradiation or ethylene oxide sterilization. The product may be packagedappropriately to maintain sterility until use.

It is not necessary to think that there is an abrupt change of localempty volume fraction at the boundary between the first region 100 andthe second region 200, nor that the boundary between first region 100and second region 200 is perfectly smooth. It is first of all possiblethat the boundary between first region 100 and second region 200 couldbe somewhat rough or irregular, such as if region 100 has a void thatbreaks or ends at the boundary, or if powder particles near the boundaryretain some of their original shape after fusing and resolidifying. Itis also not necessary that the local empty volume fraction of secondregion 200 near the interface with region 100 be identical to the localempty volume fraction of second region 200 a few strut-lengths away,near the bone-facing surface of second region 200. The local emptyvolume fraction of second region 200 could be designed to vary as mightbe desired along the path from the interface between first region 100and second region 200, to the nearby bone-facing surface of secondregion 200.

Any of the described features can be used alone or in combination withany other features. Cantilevers could be used in combination with anyother described feature. Any of the described features can be used toenhance mechanical fixation of the implant relative to bone, either atthe time of implantation or at some time after surgery after eitherpartial or full healing and bone ingrowth. Any of the described featurescan be optimized for local empty volume fraction, local average strutlength, interconnectivity between openings, and external surfaceroughness within a specified boundary. Any of the described features canbe formed to generate macroscopic structures as features of the boundarysurface to provide for mechanical fixation. Any of the describedfeatures may serve to prevent rotation, subsidence, or expulsion, andfurther may serve as a mechanical fixation and porous mesh for biologicfixation by bone ingrowth or ongrowth.

As discussed herein, it is possible to use described features orapparatus with generally any shape of implant for generally any part ofthe body. It is possible to use more than one of the techniques orfeatures or apparatus described herein, in any combination. Allreferenced documents are incorporated by reference herein in theirentirety. Although embodiments have been disclosed herein, it is desiredthat the scope be limited only by the attached claims.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e., “one or more” ofthe elements so conjoined. Other elements may optionally be presentother than the elements specifically identified by the “and/or” clause,whether related or unrelated to those elements specifically identified.Thus, as a non-limiting example, a reference to “A and/or B”, when usedin conjunction with open-ended language such as “comprising” can refer,in one embodiment, to A only (optionally including elements other thanB); in another embodiment, to B only (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of” or“exactly one of” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

It should also be understood that, unless clearly indicated to thecontrary, in any methods claimed herein that include more than one stepor act, the order of the steps or acts of the method is not necessarilylimited to the order in which the steps or acts of the method arerecited.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively, as set forth in the United States Patent Office Manual ofPatent Examining Procedures, Section 2111.03.

We claim:
 1. An implantable device, comprising: a first region that issubstantially solid; and a second region, adjacent to said first region,said second region comprising a plurality of interconnected struts, someof said struts joining said first region, said struts having an averagestrut length, said struts defining openings between said struts throughwhich bone can grow, wherein said second region comprises struts thatare connected at both of their ends to other struts and are outermoststruts and define an exterior having a bone-facing enveloping surface,wherein said bone-facing enveloping surface is at least approximately ahemisphere having a pole, an equator, and a plurality of macroscopicsurface-interrupting features projecting outwardly from said hemispherealong a direction between said pole and said equator, at least one ofsaid plurality of macroscopic surface-interrupting features comprisessome of said interconnected struts, and wherein said at least onemacroscopic surface-interrupting feature increases in height away fromsaid hemisphere in said direction from said pole towards said equator.2. The implantable device of claim 1, wherein said at least onemacroscopic surface-interrupting feature is selected from the groupconsisting of an engagement ridge, a crest, a fin, a fin having at leastone tooth, and a divertor structure.
 3. The implantable device of claim2, wherein said at least one macroscopic surface-interrupting feature issaid fin having said at least one tooth.
 4. The implantable device ofclaim 1, wherein said at least one macroscopic surface-interruptingfeature has a cross-sectional shape that is generally triangular.
 5. Theimplantable device of claim 1, wherein said plurality of macroscopicsurface-interrupting features are distributed in a regular pattern onsaid implantable device.
 6. The implantable device of claim 1, whereinsaid at least one macroscopic surface-interrupting feature has a leadingend with respect to a direction of advancement of said implantabledevice, and said leading end is sharp, and wherein said at least onemacroscopic surface-interrupting feature has a trailing end with respectto said direction of advancement of said implantable device, and saidtrailing end is blunt.
 7. The implantable device of claim 1, whereinwhere said first region has an overall density that is at least 90% of asolid density of a material from which said first region is made.
 8. Theimplantable device of claim 1, wherein said at least one macroscopicsurface-interrupting feature has a thickness of at least one of saidaverage strut length.
 9. An implantable device, comprising: a firstregion that is substantially solid; and a second region, adjacent tosaid first region, said second region comprising a plurality ofinterconnected struts, some of said struts joining said first region,said struts having an average strut length, said struts definingopenings between said struts through which bone can grow, wherein saidsecond region comprises struts that are connected at both of their endsto other struts and are outermost struts and define an exterior having abone-facing enveloping surface, wherein said bone-facing envelopingsurface is at least approximately a hemisphere having an equator, apole, and a plurality of macroscopic surface-interrupting featuresprojecting outwardly from said hemisphere, and at least one of saidplurality of macroscopic surface-interrupting features comprises some ofsaid interconnected struts, said plurality of macroscopicsurface-interrupting features exist at or near said equator of saidbone-facing enveloping surface but a region closer to said pole of saidbone-facing enveloping surface is free of said plurality of macroscopicsurface-interrupting features, and wherein said second region has avariation of local empty volume fraction such that a local empty volumefraction near said pole is greater than a local empty volume fractionnear said equator, or said local average strut length near said pole isgreater than said local average strut length near said equator.
 10. Theimplantable device of claim 9, wherein said at least one macroscopicsurface-interrupting feature increases in height away from saidhemisphere in a direction from said pole towards said equator.
 11. Theimplantable device of claim 9, wherein said second region has avariation of local empty volume fraction within said second region, orsaid second region has a variation of local average strut length withinsaid second region, or both.
 12. An implantable device, comprising: afirst region that is substantially solid; and a second region, adjacentto said first region, said second region comprising a plurality ofinterconnected struts, some of said struts joining said first region,said struts having an average strut length, said struts definingopenings between said struts through which bone can grow, wherein saidsecond region comprises struts that are connected at both of their endsto other struts and are outermost struts and define an exterior having abone-facing enveloping surface, wherein said second region has avariation of local empty volume fraction within said second region, orsaid second region has a variation of local average strut length withinsaid second region, or both, and wherein said second region comprises amajority external enveloping surface and a macroscopicsurface-interrupting feature, and wherein said majority externalenveloping surface is at least approximately a hemisphere having a poleand an equator, and wherein said second region has a variation of localempty volume fraction such that a local empty volume fraction near saidpole is greater than a local empty volume fraction near said equator, orsaid local average strut length near said pole is greater than saidlocal average strut length near said equator.
 13. The implantable deviceof claim 12, wherein said local empty volume fraction is greater nearsaid bone-facing enveloping surface and is lesser near an interfacebetween said first region and said second region, or wherein said localaverage strut length is greater near said bone-facing enveloping surfaceand is lesser near said interface between said first region and saidsecond region.
 14. The implantable device of claim 12, wherein saidsecond region comprises a majority external enveloping surface and amacroscopic surface-interrupting feature, and wherein said variation ofsaid local empty volume fraction or said variation of said local averagestrut length exists within said macroscopic surface-interruptingfeature.
 15. An implantable device, comprising: a first region that issubstantially solid; and a second region, adjacent to said first region,said second region comprising a plurality of interconnected struts, someof said struts joining said first region, said struts having an averagestrut length, said struts defining openings between said struts throughwhich bone can grow, wherein said second region comprises struts thatare connected at both of their ends to other struts and are outermoststruts and define an exterior having a bone-facing enveloping surface,wherein said bone-facing enveloping surface is at least approximately ahemisphere having a pole, an equator, and a plurality of macroscopicsurface-interrupting features projecting outwardly from said hemispherealong a direction between said pole and said equator, at least one ofsaid plurality of macroscopic surface-interrupting features comprisessome of said interconnected struts, wherein said at least onemacroscopic surface-interrupting feature is selected from the groupconsisting of an engagement ridge, a crest, a fin, a fin having at leastone tooth, and a divertor structure, and wherein said at least onemacroscopic surface-interrupting feature is said fin having said atleast one tooth.
 16. The implantable device of claim 15, wherein said atleast one macroscopic surface-interrupting feature has a cross-sectionalshape that is generally triangular.
 17. The implantable device of claim15, wherein said plurality of macroscopic surface-interrupting featuresare distributed in a regular pattern on said implantable device.
 18. Theimplantable device of claim 15, wherein said at least one macroscopicsurface-interrupting feature has a leading end with respect to adirection of advancement of said implantable device, and said leadingend is sharp, and wherein said at least one macroscopicsurface-interrupting feature has a trailing end with respect to saiddirection of advancement of said implantable device, and said trailingend is blunt.
 19. The implantable device of claim 15, wherein where saidfirst region has an overall density that is at least 90% of a soliddensity of a material from which said first region is made.
 20. Theimplantable device of claim 15, wherein said at least one macroscopicsurface-interrupting feature has a thickness of at least one of saidaverage strut length.
 21. An implantable device, comprising: a firstregion that is substantially solid; and a second region, adjacent tosaid first region, said second region comprising a plurality ofinterconnected struts, some of said struts joining said first region,said struts having an average strut length, said struts definingopenings between said struts through which bone can grow, wherein saidsecond region comprises struts that are connected at both of their endsto other struts and are outermost struts and define an exterior having abone-facing enveloping surface, wherein said bone-facing envelopingsurface is at least approximately a hemisphere having an equator, apole, and a plurality of macroscopic surface-interrupting featuresprojecting outwardly from said hemisphere, and at least one of saidplurality of macroscopic surface-interrupting features comprises some ofsaid interconnected struts, said plurality of macroscopicsurface-interrupting features exist at or near said equator of saidbone-facing enveloping surface but a region closer to said pole of saidbone-facing enveloping surface is free of said plurality of macroscopicsurface-interrupting features, and wherein said at least one macroscopicsurface-interrupting feature increases in height away from saidhemisphere in a direction from said pole towards said equator.
 22. Theimplantable device of claim 21, wherein said second region has avariation of local empty volume fraction within said second region, orsaid second region has a variation of local average strut length withinsaid second region, or both.